This is problably not the main way to do this, but I like using examples with easy numbers to solve problems like these.
I'm going to pretend that the length of square A's side is 4.
Square B's side length, then, will be 3, because 4*3/4=3.
The area of square A is 16, because 4*4=16
The area of square B is 9 because 3*3=9.
The ratio of the areas is 9/16.
Hope this helps!
