Sides of a square are all the same.
4(x-2) = (5x-20)
Distribute the left side:
4x -8 = 5x-20
Subtract 4x from both sides:
-8 = x -20
Add 20 to both sides:
X = 12
Now replace x with 12 and solve for the length:
5(12) -20 = 60-20 = 40
The sides are 40 cm long.