There are only two firms in an industry with demand curves q₁ = 30 - P and q₂ = 30 - P. Both have no fixed costs and each has a marginal cost of 10 per unit produced. If they behave as profit maximizing price takers, each produces 10 units and sells them at a price of 10 so that each firm makes zero economic profits. If they form a cartel, their inverse demand curve is

Q = 60 - 2P.

Q = 30 - P.

P = 60 - 2Q.

P = 30 - Q/2.