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. 

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

This question is asking what can we add to $\displaystyle 13$ to get to $\displaystyle 14$. 

We can count up from $\displaystyle 13$ until we get to $\displaystyle 14$, and count the number of numbers we had to add after $\displaystyle 13$. 

$\displaystyle 13,14$

We have to add $\displaystyle 1$ numbers to get from $\displaystyle 13$ to $\displaystyle 14$. 

Or we can subtract to find the missing number. 

$\displaystyle \frac{\begin{array}[b]{r}14\\ -\ \ 13\end{array}}{ \ \ \ \ \ \ \space 1}$