Area is defined as L x W L as shown in the picture is 8x -10
W = 2x (wall) + 2x (pool) = 4x
so L * W = (8x-10) (4x) = 32x^2 - 40x = Patio Area
Then substitue 9 for x to get the second answer...... (32*81-40*9 = 2232 sq ft
2232 sqft x $10 /sqft = $22320