Suppose a service is produced and sold in a competitive market has only negative externalities that are estimated by 10 dollars at each unit of the production, there are no external benefits. if MPB = MPC = 50 dollars when the quantity produced reaches to 150 units. And When quantity produced reaches to 100 units, both MSC & MPC are equal. According to these data answer the following: 1- Determine graphically and numerically the equilibriums point of the free market system. 2- Determine the corrective tax or subsidy per unit that is required for achieving efficiency and determine the efficient equilibrium. 3- Determine the consumer price, the producer price and the total subsidy or the total tax at the efficient output. 4- Determine the net gain or loss according to the government policy.