The revenue (in thousands of dollars) from producing x units of an item is modeled by R(x)=9x-0.002x. a. Find the average rate of change in revenue as x changes from 1003 to 1005. b. Find the marginal revenue at x=1500. a. The average rate of change in revenue is dollars per unit. (Do not round until the final answer. Then round to the nearest dollar as needed.)