The daily cost C, in RM, of producing a product is

C(x)=1000+72x-0.06x^2
(0 more & equal x less & equal 60)

where x represents the number of product produced.

a) Find the daily cost of producing 50 units
b) Find the marginal cost function.
c) Find Cā€™(50) and interpret its meaning.
d) Use the marginal cost to estimate the cost of producing 51 units.
e) Find the actual cost of producing 51 units. Compare the actual cost of making 51 units to the estimated cost of producing 51 units found in part d).
f) Find the average cost of producing 51 units.

i need help for question c), d) & e).
Because at c) i don't know what to intrepret. at d) my ans is not same with the given ans. at d) i don't know what to say when comparing.

given ans.
8.a) 4450 b) 72 ā€“ 0.12x c) 66 d) 4516 e) 4514.94 f) 88.55