a) In equilibrium the supply and demand curves will intersect in the equilibrium point at Q0 and P0.
b) In the long run all firms receive normal (zero) profits, because at profit-maximizing point MR = MC = P = ATC.
c) In this case the demand for corn will decrease, as a result both equilibrium price and quantity will decrease. The firm will face losses, because P < ATC.
d) In the lonfg run the supply will decrease, because some firms will exit the industry, so the equilibrium quantity will decrease, but the equilibrium price will increase back. As a result all remaining firms will receice normal (zero) profits again.