The market demand for a pair of duopolists is given as P = 72 - 3Q, where Q= Q1 + Q2. Total costs equal 24Q for each firm. Determine the equilibrium price, each firm's output and profit for the following models:
a. Shared Monopoly
b. Cournot Duoplists (each rival assumes output is fixed)
c. Stackelberg Duopolists (assume firm one is the leader)
d. Bertrand Duopolists (competitive case)