I need help plz answer all of the questions in the image thank you in advanced Note:(Correct answer gets brainiest plz make sure and explain the best as possible)

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.