Here are some questions that i just don't understand, please show working out.

Thanks

Q1. ) A skateboard manufacturer finds that the cost $C of making X skateboards per day is given by C(x) = x^2-24x+244.

a)How many skateboards should be made per day to minimise the cost of production?

Q2) The driver of a car travelling downhill on a road applied the brakes. The speed (s) of the car in kmph, t seconds after the brakes were applied is given by s(t)= -4t^2 +12t+80.

a) How fast was the car travelling when the driver applied the brakes?

Mr F says: Substitute t = 0.
b) After how many seconds was the speed of the car 88 kmph? Can you explain your answer?

Mr F says: Solve 88 = -4t^2 + 12t + 80.
c) After how many seconds did the car reach its maximum speed?

d) What was the maximum speed reached?

Q3.) The hourly profit ($P) obtained from operating a fleet of n taxis is given by P(n) = 84n-45-2n^2.

a) What number of taxis gives the maximum hourly profit?

b) What is the maximum hourly profit/

c) HOw much money is lost per hour if no taxis are on the road?

Mr F says: Substitute n = 0.
Q4.) The temperature T Celsius in a greenhour t hours after susk (7.00 pm) is given by T(t)= 1/4 t^2-5t+30, (t<20)

a)what was the temperature in the greenhouse at dusk?

Mr F says: Substitute t = 0.
b) At what time was the temperature at a minimum?

c) What was the minimum temperature?

Thanks guys, i just really need ot know how to do it pronto.