A perfectly competitive market has demand and supply as follows: QD = 90 – 20P QS = 10P Which of the following is correct?

a) If price equals 4, there will be excess demand, and the quantity traded equals 10.

b) There is excess demand at any price below 3.

c) If price equals 2, there will be excess demand, and the quantity traded equals 50.

d) The equilibrium quantity equals 3