(a) Before the renewable fuels mandate, the corn market is in equilibrium at (Q_c1, P_c1), where the initial demand curve D_c1 and supply curve S_c1 intersect. The direct effect of the renewable fuels mandate shifts demand out to D_c2. Because the mandate also increases the price of wheat, however, the demand for corn continues to shift out until general equilibrium is reached at (Q_cF, P_cF), where D_cF intersects S_c1.(b) Wheat, a substitute good for corn, is at an initial equilibrium of (Q_w1, P_w1), where the initial demand curve D_w1 and supply curve S_w1 intersect. When the renewable fuels mandate increases corn prices, the demand for wheat increases to D_w2. The subsequent increases in corn prices continue to shift out the demand for wheat until general equilibrium is reached at (Q_wF, P_wF), where D_wF intersects S_w1.