Answer:
C(x) = 0.004x^2 + 90x + $8,500
Step-by-step explanation:
In order to find the to monthly cost C(x) incurred, the marginal cost C '(x) = 0.008x + 90 will have to be integrated using integral calculus as follows:
Where C is the constant or fixed costs
The equation above can be further solved as follows:

Since fixed costs is $8500/month, we substitute for C to obtain the the total monthly cost C(x) incurred by Carlota in manufacturing x guitars/month as follows:
C(x) = 0.004x^2 + 90x + $8,500