Answer and Explanation:
When there is price fixing between two competitors, if one competitor chooses to fix the price it should not exceed competutors marginal cost and should be above his marginal cost.
Since the price fixing of $10 will be fined then the ideal price to maximize the profit would be below the competitors price $ and above his marginal cost $.
The ideak price to maximize profits would be (competitors price $ + his marginal cost $)/2, This price would be above his marginal cost and below competitors price.