The market demand in a Bertrand duopoly is P = 15 - 4Q, and the marginal costs are $3. Fixed costs are zero for both firms. Which of the following statement(s) is/are true?

a.P = $3.

b.P = $10.

c. P = $15.

d. None of the statements associated with this question are correct.

I choose A as my answer because fixed cost was zero. If I'm wrong, can you please explain to me how to solve this...