During the first 1/2 hour, the employees of a machine shop prepare the work area for the day’s work. After that, they turn out 10 precision machine parts per hour, so the output after t hours is f (t) machine parts, where f (t) = 10(t - 1/2) = 10t - 5, 12 … t … 8. The total cost of producing x machine parts is C(x) dollars, where C(x) = .1x2 + 25x + 200.

(a) Express the total cost as a (composite) function of t.

(b) What is the cost of the first 4 hours of operation?