12. [-/5 Points] DETAILS HARMATHAP12 10.1.054. 0/15 Submissions Used Suppose the average costs of a mining operation depend on the number of machines used, and average costs, In dollars, are given by C(x) = 2900x + 2,610,000 X > O , X where x is the number of machines used. (a) Find the critical values of C(x) that lie in the domain of the problem. (Enter your answers as a comma-separated list.) X (b) Over what interval in the domain do average costs decrease? (Enter your answer using interval notation.) (c) Over what interval in the domain do average costs increase? (Enter your answer using interval notation.) (d) How many machines give minimum average costs? machines (e) What is the minimum average cost? $ Need Help? Read It