Question 93119
You are on the right path:
x(x + 3) = 180
x^2 + 3x = 180
x^2 + 3x - 180 = 0
(x + 15)(x - 12) = 0
x = -15 and x = 12
Lenght can not be considered as negative ... x = 12
Length = 12 + 3 = 15 inches
Width = 12 inches