Suppose the supply curve of portable radio rentals in Golden Gate Park is given by: P = 5 + 0.1Q, where P is the daily rent per unit in dollars and Q is the volume of units rented in hundreds per day. The demand curve for portable radios is: P = 20 – 0.2Q. If each portable radio imposes $2.70 per day in noise costs on others, by how much will the equilibrium number of portable radios rented exceed the socially optimal number?