36x 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 produced. 3 x te (a) Find the cost function, given that the company incurs a fixed cost of $14,000 even if no units are built. (b) The company will seek a new source of investment income if the cost is more than $19,000 to produce 5 units. Should they seek this new source? (a) What substitution should be used to determine the cost function? Use the quantity in the denominator as the substitution, u = 3x +e . so that du = (6x ) dx. The cost function is C(x)=