Use the distributive property to find an equivalent expression
9(3x - 1)
this confuses me!

Suppose that the price p (in dollars) and the weekly sales x (in thousands of units) of a certain commodity satisfy the demand equation 4p cubedplusx squaredequals38 comma 400. determine the rate at which sales are changing at a time when xequals80, pequals20, and the price is falling at the rate of $.20 per week.

How do i do this activity, is appreciated

Just tell me how to set up the equation.