8. Demand and supply curves can also be represented with equations. Suppose that the quantity demanded, QD, is represented by the following equation:

QD = 90 − 2P The quantity supplied, QS, is represented by the equation QS = P

a. Find the equilibrium price and quantity.

(Hint: Set QD = QS and solve for the price, P, and then plug your result back into either of the original equations to find Q.)

b. Suppose that the price is $20. Determine QD and QS.

c. At a price of $20, is there a surplus or a shortage in the market?

d. Given your answer in part (c), will the price rise or fall in order to find the equilibrium point?