The area of a rectangular deck can be modeled by f (x) = 2x3 + 30x2 - 6x - 90. If x + 15 represents the width, which expression represents the length?

Area of a rectangle = length * width

f (x) = 2x ³ + 30x² - 6x - 90

f (x) = 2 (x³ + 15x² - 3x - 45)

f (x) = 2 (x² (x + 15) - 3 (x+15))

f (x) = 2 (x²-3) (x+15)

If width = x+15, then

length = 2 (x²-3) = 2x²-6

Divide f (x) by x + 15

this comes to 2x^2 - 6 which represents the length