This question is asking what can we add to \(\displaystyle 4\) to get to \(\displaystyle 13\). 

We can count up from \(\displaystyle 4\) until we get to \(\displaystyle 13\), and count the number of numbers we had to add after \(\displaystyle 4\). 

\(\displaystyle 4,5,6,7,8,9,10,11,12,13\)

We have to add \(\displaystyle 9\) numbers to get from \(\displaystyle 4\) to \(\displaystyle 13\). 

Or we can subtract to find the missing number. 

\(\displaystyle \frac{\begin{array}[b]{r}13\\ -\ \ 4\end{array}}{ \ \ \ \ \space 9}\)

This question is asking what can we add to \(\displaystyle 5\) to get to \(\displaystyle 11\). 

We can count up from \(\displaystyle 5\) until we get to \(\displaystyle 11\), and count the number of numbers we had to add after \(\displaystyle 5\). 

\(\displaystyle 5,6,7,8,9,10,11\)

We have to add \(\displaystyle 6\) numbers to get from \(\displaystyle 5\) to \(\displaystyle 11\). 

Or we can subtract to find the missing number. 

\(\displaystyle \frac{\begin{array}[b]{r}11\\ -\ \ 5\end{array}}{ \ \ \ \ \space 6}\)

This question is asking what can we add to \(\displaystyle 2\) to get to \(\displaystyle 10\). 

We can count up from \(\displaystyle 2\) until we get to \(\displaystyle 10\), and count the number of numbers we had to add after \(\displaystyle 2\). 

\(\displaystyle 2,3,4,5,6,7,8,9,10\)

We have to add \(\displaystyle 8\) numbers to get from \(\displaystyle 2\) to \(\displaystyle 10\). 

Or we can subtract to find the missing number. 

\(\displaystyle \frac{\begin{array}[b]{r}10\\ -\ \ 2\end{array}}{ \ \ \ \ \space 8}\)

This question is asking what can we add to \(\displaystyle 6\) to get to \(\displaystyle 13\). 

We can count up from \(\displaystyle 6\) until we get to \(\displaystyle 13\), and count the number of numbers we had to add after \(\displaystyle 6\). 

\(\displaystyle 6,7,8,9,10,11,12,13\)

We have to add \(\displaystyle 7\) numbers to get from \(\displaystyle 6\) to \(\displaystyle 13\). 

Or we can subtract to find the missing number. 

\(\displaystyle \frac{\begin{array}[b]{r}13\\ -\ \ 6\end{array}}{ \ \ \ \ \space 7}\)

 This question is asking what can we add to \(\displaystyle 7\) to get to \(\displaystyle 9\). 

We can count up from \(\displaystyle 7\) until we get to \(\displaystyle 9\), and count the number of numbers we had to add after \(\displaystyle 7\). 

\(\displaystyle 7,8,9\)

We have to add \(\displaystyle 2\) numbers to get from \(\displaystyle 7\) to \(\displaystyle 9\). 

Or we can subtract to find the missing number. 

\(\displaystyle \frac{\begin{array}[b]{r}9\\ -\ \ 7\end{array}}{ \ \ \ \ \space 2}\)

This question is asking what can we add to \(\displaystyle 8\) to get to \(\displaystyle 14\). 

We can count up from \(\displaystyle 8\) until we get to \(\displaystyle 14\), and count the number of numbers we had to add after \(\displaystyle 8\). 

\(\displaystyle 8,9,10,11,12,13,14\)

We have to add \(\displaystyle 6\) numbers to get from \(\displaystyle 8\) to \(\displaystyle 14\). 

Or we can subtract to find the missing number. 

\(\displaystyle \frac{\begin{array}[b]{r}14\\ -\ \ 8\end{array}}{ \ \ \ \ \space 6}\)

This question is asking what can we add to \(\displaystyle 9\) to get to \(\displaystyle 20\). 

We can count up from \(\displaystyle 9\) until we get to \(\displaystyle 20\), and count the number of numbers we had to add after \(\displaystyle 9\). 

\(\displaystyle 9,10,11,12,13,14,15,16,17,18,19,20\)

We have to add \(\displaystyle 11\) numbers to get from \(\displaystyle 9\) to \(\displaystyle 20\). 

Or we can subtract to find the missing number. 

\(\displaystyle \frac{\begin{array}[b]{r}20\\ -\ \ 9\end{array}}{ \ \ \ \ \space 11}\)

This question is asking what can we add to \(\displaystyle 10\) to get to \(\displaystyle 15\). 

We can count up from \(\displaystyle 10\) until we get to \(\displaystyle 15\), and count the number of numbers we had to add after \(\displaystyle 10\). 

\(\displaystyle 10,11,12,13,14,15\)

We have to add \(\displaystyle 5\) numbers to get from \(\displaystyle 10\) to \(\displaystyle 15\). 

Or we can subtract to find the missing number. 

\(\displaystyle \frac{\begin{array}[b]{r}15\\ -\ \ 10\end{array}}{ \ \ \ \ \ \ \space 5}\)

This question is asking what can we add to \(\displaystyle 11\) to get to \(\displaystyle 19\). 

We can count up from \(\displaystyle 11\) until we get to \(\displaystyle 19\), and count the number of numbers we had to add after \(\displaystyle 11\). 

\(\displaystyle 11,12,13,14,15,16,17,18,19\)

We have to add \(\displaystyle 8\) numbers to get from \(\displaystyle 11\) to \(\displaystyle 19\). 

Or we can subtract to find the missing number. 

\(\displaystyle \frac{\begin{array}[b]{r}19\\ -\ \ 11\end{array}}{ \ \ \ \ \ \ \space 8}\)

This question is asking what can we add to \(\displaystyle 12\) to get to \(\displaystyle 18\). 

We can count up from \(\displaystyle 12\) until we get to \(\displaystyle 18\), and count the number of numbers we had to add after \(\displaystyle 12\). 

\(\displaystyle 12,13,14,15,16,17,18\)

We have to add \(\displaystyle 6\) numbers to get from \(\displaystyle 12\) to \(\displaystyle 18\). 

Or we can subtract to find the missing number. 

\(\displaystyle \frac{\begin{array}[b]{r}18\\ -\ \ 12\end{array}}{ \ \ \ \ \ \ \space 6}\)