Explanation:
L = length
W = width
L = W + 9
A = 112 = LW = (W+9)W
So,
W2 + 9W = 112
W2 + 9W - 112 = 0
Factoring
(W-7)(W+16) = 0
W = 7, -16
We discard W = -16, since a measurement cannot be negative.
W = 7
And since L = W + 9, then L = 7 + 9 = 16
This is a 16x7 rectangle