Hello!
The perimeter is sum of all sides of a figure. In this figure, we have unknown sides. To find the unknown sides, we have to use the sides that we know. By adding and subtracting numbers, you can find the other sides. See the image below, to see how I did it.
I also have another practice problem, for you to practice on your own if you want to.
Also, mishap on picture, The answer is 58.