Write an expression for the total surface area (sa) of a rectangular prism whose base is a square with side of length x and height of y.

For this case we have the following expression:
 S.A = 2x ^ 2 + 2x *y + 2x * y
 Rewriting we have:
 S.A = 2x ^ 2 + 4x *y
 S.A = 2 (x ^ 2 + 2x * y)
 Where,
 x: side length of a square base
 y: height of the prism
 
 an expression for the total Surface Area (SA) of a rectangular prism is:
 S.A = 2 (x ^ 2 + 2x * y)

3/a x - 4 = 20

3/a x = 24

a=1
x=8