Omg if you know how to do this lemme kno but this is urgent

Simplify (a/b - b/a) times (a - a^2/a+b) a - a^2/a=b is a mixed number

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.

Emily is entering a bicycle race for charity. her mother pledges $0.90 for every 0.75 mile she bikes. if emily bikes 18 miles, how much will her mother donate?