I dont know how to solve plz help

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.

What is the range? can’t seem to find it out

Ineed to know the ordered pairs for this equation i need the answer quick because it’s a timed test