Marginal Cost

[TheNextOne]

A manufacturer of custom furniture finds that when 18 wood rocking chairs are
made per day, the average cost is $200 and the marginal cost is $100. Based on this, estimate the total cost to make 19 chairs.

How would you evaluate this?

I did the following:

200= Total Cost/q
100= MC

Therfore, TC - 200q= 100
When q = 19, TC= 3700

I dont think this is right. Can anybody give me a hint?

 

[Gene]

Your answer is correct but I think what they want is
f'(q)=100
f(q)=100q+c
f(18)=3600
c=1800
f(q)=100q+1800
f(19)=1900+1800 = 3700