4. (20 pts.) Economics. The flow demanded on a highway is given by the function D(t, p) = 320 80t 10p veh/hr, (3) where t is the travel time in hours and p is the toll. The link performance function for the highway is T (q) = .2 + (q/300)2 hr, (4) 4(a) (10 pts.) If there is no toll, what is the equilibrium flow and travel time on the where q (veh/hr) is the flow. highway? 4(a) 4(b) (10 pts.) What toll would make the equilibrium travel time equal to 0.5 hrs