length of pool, L = 10 + W
width of pool, W
pool area = W(10+W)
backyard is square shaped.. sides are equal
backyard side length, S = 5 + 3W
Area backyard = (5+3W)(5+3W)
subtract pool area
Area surrounding pool
= (5+3W)(5+3W) - W(10+W)
simplify the expression, foil
= 25 + 30W + 9W^2 - 10W - W^2
combine like terms
A = 8W^2 + 20W + 25