A company manufactures downhill skis. The research department produced the marginal cost graph shown below, where C(x) is in dollars and x is the number of skis produced per week. Estimate the increase in cost going from a production level of 200 to 600 pairs of skis per week. Use left and right sums over two equal subintervals. Replace the question marks with the values of Lz and Rz as appropriate:

C'(x)dx=?200 600 200 400