33.90 divided by 10.2

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.

For the equations below which statement is true ?

Hi, can anyone show me how to do this problem? 100 points for this. in advance