Find the sum or difference.

$7.2+13.7$

Two numbers with similar signs get added and the resulting number carries the similar sign. So, if two numbers with positive signs being added, the resulting sum will be positive as well. And if two numbers with negative signs being added, then the resulting sum will be negative as well.

If two positive numbers 2 and 3 are being added, then the resulting sum will be $2+3=5$, which is positive as well.

And if two negative numbers $-2$ and $-3$ are being added, then the resulting sum will be$\left(-2\right)+\left(-3\right)=-5$, which is negative as well.

The numbers 7.2 and 13.7 are positive numbers, so they will get added and the resulting number will be positive as well.

The sum of the numbers can be computed as shown below,

$\begin{array}{l}7.2\\ \underset{\_}{+13.7}\\ 20.9\end{array}$

Thus, the sum of the given numbers is $20.9$.