A rectangle picture window is 4 ft. by 7 ft. Polly wants to put a trim molding around the window. How many feet of molding should she buy?

Do I just add both sides to get my answer?

Well a picture frame has 4 sides so you need to add the length of all of them.

In other words: 2 lengths + 2 widths

the answer is: 4 + 4 + 7 + 7 = 22ft

You are being asked, in effect, to calculate the perimeter of the photo frame.

Ok,
Hope that helps!