Greg F. answered 03/11/19
SAT Expert|Master the SAT Easily|Get into your dream school
Three things you have to know to answer this problem: that the lengths of all sides of a square are the same, that the perimeter of a shape is the sum of all its sides, and that the area of square is the length times the width.
So if the perimeter is supposed to be 40, and there are four sides to a square and they are all the same length, then how long would each side be? Once you figure that out, then you would just multiply two of the sides together to find the area.
Good luck!