A chemical company can produce Q units of a chemical H, with marginal costs of MC = 9 + Q, and can distribute the chemical at marketing marginal costs of MC = 1. The demand for H is given by P = 30 - 1.5Q. If an external market exists where H can be bought or sold without marketing expenses for $13, how much H should the firm produce?
A. 0 units
B. 4 units
C. 5 units
D. 7 units
E. 10 units