The current area is 15 x 9 = 135 square feet.
He wants to increase both the length and width by X:
Set up an equation:
(15 +x) * (9 +x) = 135 * 2
Simplify :
x^2 + 24x + 135 = 270
Subtract 270 from both sides:
x^2 + 24x - 135 = 0
Use the quadratic formula to solve for x:
-24 +/- √(24^2 - 4(1*-135) / 2*1
x = 4.7 or -28.7
The answer has to be a positive value, so x = 4.7 feet.
