The weekly cost C of producing x units in a manufacturing process is given by
The number of units x produced in t hours is given by
(a) The composite function C(x(t)) is given by
The function C(x(t)) gives us the cost of production for t hours.
(b) The number of units produced in 4 hours is given by
200 units will be produced in 4 hours.
(c) Let us graph the function C(x(t)) = 3000t + 750 to find the value of t for which the cost increases to $15,000
As you can see, the value of t is 4.75 hours when the cost is $15,000.
Therefore, 4.75 hours must elapse until the cost increases to $15,000.