Suppose the supply curve of noisy surf-ski rentals on Sandy Bay beach is given by p=5+0.1xQ where p is the daily rent per unit in dollars and is the volume of units rented in hundreds per day. The demand curve for surf skis is p=20-0.2xQ . If each surf ski imposes $3 per day in noise costs on others, by how much will the equilibrium number of surf skis rented exceed the socially optimal number?