I need help with number 3 plzzz fast

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.

Solve 2x+y=3 x+y=5 in substitution method

Find the volume of the solid bounded by the plane z=0 and the paraboloid z=1-x^2 –y^2