Answer: C. Firm A reduces the price to $7 causing Firm B to reduce its price to $4.50.
Step-by-step explanation:
Since firm A is impatient to earn more profits and Firm B wishes to last in the business for the long-run, then Firm A will reduce the price to $7 causing Firm B to reduce its price to $4.50.
Since Firm A reduces the price to $7, this will lead to an increase in the quantity demanded of the product and therefore the firm can earn more profit. On the other hand, firm B will reduce its price to a point where the price meets the marginal cost which is $4.50.