Suppose the total cost of producing q units of some commodity is given by the cost function C(q) = 0.002q + 2q + 70, where q is the number of units produced, and C(q) is the total cost, in dollars, to produce q units. A) Find a simplified expression for the marginal cost function. (Be sure to use the proper variable in your answer.) MC(q) B) What is the exact rate of change of costs when 250 units have been produced? The rate of change is dollars per item. (Your answer may be negative.)