4. (5 points) Given a total-revenue function R(x) = 1000vx2 - 0.3x and a total-cost function C(x) = 1600vx2 + 3 + 500, both in thousands of dollars, find the rate at which total profit is changing when x items have been produced and sold.5. (5 points) Suppose that the demand function for a product is given by 75, 000 D0?) = p , and that price p is a function of time given by p = 1.41; + 9, Where t is in days. (i) Find the demand as a function of time t. (ii) Find the rate of change of the quantity demanded when t = 120 days