Each penny is worth $\displaystyle 1\cent$ and each nickel is worth $\displaystyle 5\cent.$

We have six pennies and three nickels. 

$\displaystyle \frac{\begin{array}[b]{r}1\cent\\ \ 1\cent\\ 1\cent\\ \ 1\cent\\ 1\cent\\ +\ 1\cent\end{array}}{ \ \ \ \space 6\cent}$ $\displaystyle \frac{\begin{array}[b]{r}5\cent\\ 5\cent\\ +\ 5\cent\end{array}}{ \ \ \space 15\cent}$

$\displaystyle \frac{\begin{array}[b]{r}6\cent\\ +\ 15\cent\end{array}}{ \ \ \ \space 21\cent}$

Each penny is worth $\displaystyle 1\cent$ and each quarter is worth $\displaystyle 25\cent.$

We have three pennies and one quarter. 

$\displaystyle \frac{\begin{array}[b]{r}1\cent\\ \ 1\cent\\ +\ 1\cent\end{array}}{ \ \ \ \space 3\cent}$ $\displaystyle 25\cent$

$\displaystyle \frac{\begin{array}[b]{r}3\cent\\ +\ 25\cent\end{array}}{ \ \ \ \space28\cent}$

Each nickel is worth $\displaystyle 5\cent$ and each dime is worth $\displaystyle 10\cent$.

We have three nickels and three dimes.

 $\displaystyle \frac{\begin{array}[b]{r}5\cent\\ \ 5\cent\\ +\ 5\cent\end{array}}{ \ \ \space 15\cent}$ $\displaystyle \frac{\begin{array}[b]{r}10\cent\\ 10\cent\\ \ +\ 10\cent\end{array}}{ \ \ \ \space 30\cent}$

$\displaystyle \frac{\begin{array}[b]{r}15\cent\\ +\ 30\cent\end{array}}{ \ \ \ \space 45\cent}$

Each quarter is worth $\displaystyle 25\cent$ and each nickel is worth $\displaystyle 5\cent$.

We have one quarter and two nickels.

 $\displaystyle 25\cent$ $\displaystyle \frac{\begin{array}[b]{r}5\cent\\ +\ 5\cent\end{array}}{ \ \ \space 10\cent}$

$\displaystyle \frac{\begin{array}[b]{r}25\cent\\ +\ 10\cent\end{array}}{ \ \ \ \space 35\cent}$

Each dime is worth $\displaystyle 10\cent$ and each penny is worth $\displaystyle 1\cent$.

We have five dimes and five pennies. 

$\displaystyle \frac{\begin{array}[b]{r}10\cent\\ \ 10\cent\\ 10\cent\\ \ 10\cent\\+\ 10\cent\end{array}}{ \ \ \ \space 50\cent}$ $\displaystyle \frac{\begin{array}[b]{r}1\cent\\ \ 1\cent\\ 1\cent\\ \ 1\cent\\+\ 1\cent\end{array}}{ \ \ \ \space 5\cent}$

$\displaystyle \frac{\begin{array}[b]{r}50\cent\\ +\ 5\cent\end{array}}{ \ \ \space 55\cent}$

Each dime is worth $\displaystyle 10\cent$ and each penny is worth $\displaystyle 1\cent$. 

We have three dimes and eight pennies. 

 $\displaystyle \frac{\begin{array}[b]{r}10\cent\\ \ 10\cent\\ +\ 10\cent\end{array}}{ \ \ \ \space 30\cent}$  $\displaystyle \frac{\begin{array}[b]{r}1\cent\\1\cent\\1\cent\\1\cent\\1\cent\\1\cent\\1\cent\\ +\ 1\cent\end{array}}{ \ \ \ \space 8\cent}$

$\displaystyle \frac{\begin{array}[b]{r}30\cent\\ +\ 8\cent\end{array}}{ \ \ \space 38\cent}$

Each dollar bill is worth $\displaystyle \$1$, each nickel is worth $\displaystyle 5\cent$ and each dime is worth $\displaystyle 10\cent$.

We have $\displaystyle 2$ dollar bills, $\displaystyle 3$ nickels, and $\displaystyle 2$ dimes.

$\displaystyle \frac{\begin{array}[b]{r}\$1\\ +\$1\end{array}}{ \ \ \space\$2}$   $\displaystyle \frac{\begin{array}[b]{r}5\cent\\5\cent\\ +\ 5\cent\end{array}}{ \ \ \space 15\cent}$   $\displaystyle \frac{\begin{array}[b]{r}10\cent\\ +\ 10\cent\end{array}}{ \ \ \ \space 20\cent}$

When we add dollars and cents, we add dollars to dollars and cents to cents. 

$\displaystyle \frac{\begin{array}[b]{r}15\cent\\ +\ 20\cent\end{array}}{ \ \ \ \space 35\cent}$ 

We have $\displaystyle \$2$ and $\displaystyle 35\cent$ which is written as $\displaystyle \$2.35$

This is an addition problem because we have the difference in height from the question. Alison is $\displaystyle 60$ inches tall and David is $\displaystyle 18$ inches taller than her, $\displaystyle 18$ is our difference. We can add our difference to Alison's height to find out how tall David is. 

$\displaystyle \frac{\begin{array}[b]{r}60\\ +\ 18\end{array}}{ \ \ \ \space 78}$

This is an addition problem because we have the difference in height from the question. The grill is $\displaystyle 52$ inches tall and fence is $\displaystyle 32$ inches taller than the grill, $\displaystyle 32$ is our difference. We can add our difference to the grill's height to find out how tall the fence is. 

$\displaystyle \frac{\begin{array}[b]{r}52\\ +\ 32\end{array}}{ \ \ \ \space 84}$

This is an addition problem because we have the difference in length from the question. The pillow is $\displaystyle 15$ inches long and couch is $\displaystyle 45$ inches longer than the pillow, $\displaystyle 45$ is our difference. We can add our difference to the pillow's length to find out how long the couch is. 

$\displaystyle \frac{\begin{array}[b]{r}45\\ +\ 15\end{array}}{ \ \ \ \space 60}$