Pls help pls

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.

Nine more than four times a number is the same as one less than twice the number. find the number?

Present age of man is 45 years, 5 years back his age was 4 times age of his son what is present age of his son?