Help PLEASE! I will make you brainlist!

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.

Can someone check if i did this correct. it’s number 4 if you’re wondering.

There are 45 questions on your math exam. you answered 810 of them correctly. how many questions did you answer correctly?