Given
c'(q)=dc/dq=0.006q^2-0.6q+70
Integrate marginal cost to get cost function
c(q)=0.002q^3-0.3q^2+70q+C (C is a constant)
Fixed cost = 2000 means that C=2000.
or
c(q)=0.002q^3-0.3q^2+70q+2000
Average cost=c(q)/q, for q=200,
=(0.002*q^3-0.3*q^2+70*q+2000)/q
=20000/200
=100
Answer: Average cost is $100