desperate please help.
The number N of cars produced at a certain factory in 1 day after t hours of operation is given by N(t) = 100 t – 5 t 2 , 0 ≤ t ≤ 10. If the cost C (in dollars) of producing N cars is C(N) = 15,000 + 8000 N , find the cost C as a function of the time t of operation of the factory.

Question

desperate please help.  
 The number N of cars produced at a certain factory in 1 day after t hours of operation is given by N(t) = 100 t – 5 t 2 , 0 ≤ t ≤ 10. If the cost C (in dollars) of producing N cars is C(N) = 15,000 + 8000 N , find the cost C as a function of the time t of operation of the factory.

anonymous · Answer

All you have to do is to plug in 100t - 5t^2 as N into 15000 + 8000N so you get
15000 + 8000 (100 t - 5 t^2) which expands into

15000 + 800000 t - 40000 t^2, 0 <= t <= 10

reemii · Answer

$C(N(t))$ is what you have to compute. as belicsss just said.
"cost at time t = cost given the number N(t) of cars at time t".