2.29. Consider the following sequence of changes in the demand and supply for cab service in some city. The price P is a price per mile, while quantity is the total length of cab rides over a month (in thousands of miles).

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January: Initial demand and supply are given by the equations Q s ! 30P " 30 (when P $ 1), and Qd ! 120 " 20P February: Due to higher prices of gasoline, the supply of cab service changed to Q s ! 30P " 60 (when P $ 2).

March: Over the spring break, the demand for taxi service was higher and therefore the demand curve was given by the equation Qd ! 140 " 20P.

a) For each month find the equilibrium price and quantity.

b) Illustrate your answer with a graph. Illustrate the equilibrium prices and quantities on the graph.