Assume that a company's marginal cost function for the manufacture of x phones per hour is

c(x) = 120 − 0.002x,

and that they sell the phone for an average wholesale price of $580. Use a Riemann sum with n = 5 subdivisions to estimate the total additional hourly profit corresponding to an increase in production and sales from 10,000 to 20,000 phones per hour. (Use a left Riemann sum to find your answer.)