The inverse demand in a Cournot duopoly is P = a − b(Q1 + Q2), and costs are C1(Q1) = c1Q1 and C2(Q2) = c2Q2. The government has imposed a per-unit tax of $t on each unit sold by each firm. The equilibrium output of each firm is the same as a situation where each firm's:
demand increases by t.
demand decreases by t.
marginal cost increases by t.
marginal cost decreases by t.