Hey guys I really need help 20 points​

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.

The graph represents the gallons of water in a water tank with respect to the number of hours since it was completely filled

4+(2+x) can you me solve this problem