I'm stuck on this one, please help.

The Hunt Corporation manufactures a stantup stapler and has determined its cost for making the product to be the following:

c(x)=0.0001x^3-0.08x^2+40x + 5000 (where c(x) is in dollars and x is number of units.)

a) Find the actual cost of producing the 201st unit.

b) Estimate the cost of producing the 201st unit using the marginal cost function.

c) Find the percent margin by comparing the estimated and actual values from part a) and b)

Thank you in advance.