We no longer assume that K is fixed at 5. We need to find the combination of K and L that minimizes cost at any level of output q. The cost-minimization rule is given by .To find the marginal product of capital, observe that increasing K by 1 unit increases q by 5L, so MPK = 5L. Similarly, observe that increasing L by 1 unit increases q by 5K, so MPL = 5K. Mathematically, and .Using these formulas in the cost-minimization rule, we obtain:.The new plant should accommodate a capital to labor ratio of 1 to 2, and this is the same regardless of the number of units produced.