12. Firm 1 produces output x with a cost function c₁(x) = x²+5. Firm 2 produces output y with a cost function c₂(y, x) = y²+ 4x. Thus, the more that firm 1 produces, the greater are firm 2's costs. Both firms face competitive product markets. The competitive price of x is $20 and the competitive price of y is $40. No new firms can enter the industry and the old ones must remain. The efficient Pigovian tax on the x good is a. $0 b. $1 c. $2 d. $3 e. $4