Find the rate of change of total revenue, cost, and profit with respect to time. Assume that R(x) and C(x) are it in dollars. n R(x) = 40x - 0.5x , C(x) = 3x + 20, when x = 25 and dx / dt = 15 units per day . .. The rate of change of total revenue is $ per day. The rate of change of total cost is $ per day. ie The rate of change of total profit is $ per day