The water usage at a car wash is modeled by the equation W(x) = 3x3 + 4x2 − 18x + 4, where W is the amount of water in cubic feet and x is the number of hours the car wash is open. The owners of the car wash want to cut back their water usage during a drought and decide to close the car wash early two days a week. The amount of decrease in water used is modeled by D(x) = x3 + 2x2 + 15, where D is the amount of water in cubic feet and x is time in hours.

Write a function, C(x), to model the water used by the car wash on a shorter day.

C(x) = 2x3 + 2x2 − 18x − 11
C(x) = 3x3 + 2x2 − 18x + 11
C(x) = 3x3 + 2x2 − 18x − 11
C(x) = 2x3 + 2x2 − 18x + 11

An equation is an expression that shows the relationship between two or more numbers and variables. An independent variable is a variable that does not depend on other variables while a dependent variable is a variable that depends on other variables.

W is the amount of water in cubic feet and x is the number of hours the car wash is open, D is the amount of decrease and C(x) is the water used by the car wash on a shorter day.

Hence:

C(x) = W(x) - D(x)

C(x) = (3x³ + 4x² − 18x + 4) - (x³ + 2x² + 15) = 2x³ + 2x² -18x -11

The water used by the car wash on a shorter day is given by C(x) = 2x³ + 2x² -18x -11

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