Can you please help me with this?

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.

Ill mark the brainliest if you me with the these three questions 7,8,9

Maria walks a round trip of 0.75 mile to school every day.how many miles will she walk in 4.5 days