Alina has a business painting houses.  Her total fixed costs are $3770 per month and include equipment and vehicles.  She currently has 3 employees and pays each employee $210 per day (assume there are a total of 22 work days each month).  She also must pay for paint per house (assume this cost is the same for each house).  She is able to paint 55 houses per month, and her average total cost is $511.  Suppose she wants to increase output.  If she hires one more employee the marginal product will be 12 houses per month (assuming no change in her fixed inputs).

Calculate the marginal cost of the 56th house.

This one might be tricky.  But this is all the information you need to calculate the answer.