Question 406015
let, A = area of rectangle
     B = area of the square
     l = length of the rectangle
     w = width of the rectangle
     s = side of the square

A = 3B
l = 15
w = s
A = l.w = 3B
15s = 3s^2
3s^2 - 15s = 0
s^2 - 5s = 0
s^2 - 5s + 25/4 = 25/4
(s - 5/2)^2 = 25/4
s - 5/2 = 5/2
Final answers:
s = 5
w = 5
l = 15