L = lengh
W = width
french reasoning ( hello from France ) !
The base of the house is a rectangle where the length of a rectangle is 8 more than the width.
=> L = W + 8
and
Its area is 240 ft sq
W x L = 240
L = W + 8
W x L = 240
=> W x (W+8) = 240
W² + 8W - 240 = 0
Δ = 8² - 4*1*(-240) = 32²
W' = (-8 + 32) / 2 = 12 ft
W'' = (-8 - 32) / 2 = impossible
at the end
W the width = 12 ft
and then the lengh = 12 + 8 = 20
area = 12 x 20 = 240 ft²