70x A company has found that the marginal cost (in thousands of dollars) to produce x central air conditioning units is C'(x) = where x is the number of units 5 x + e produced. (a) Find the cost function, given that the company incurs a fixed cost of $16,000 even if no units are built. (b) The company will seek a new source of investment income if the cost is more than $22,000 to produce 5 units. Should they seek this new source? (a) What substitution should be used to determine the cost function? Use the quantity as the substitution, u = , so that du=