Final answer:
The firm in an unregulated monopolist will optimally produce 40 million units.
Step-by-step explanation:
In an unregulated monopoly, the firm will optimally produce at the level where marginal revenue (MR) equals marginal cost (MC). This is the point where the firm maximizes its profits. Based on the given options, the correct answer is 40 million units (a), since that is the quantity at which MR equals MC.