Market demand and supply of a good is shown by QB = 2,160 - 180P and QS = -2400 + 300P where QD, QS and P stand for quantity demanded, quantity supplied and price respectively.
(a) derive market equilibrium and illustrate it graphically.
(b) Derive the market equilibrium in the presence of a unit tax of $4 and illustrate the after-tax market equilibrium graphically.