I am not sure how to use the inverse speed function in this to solve this problem. I got the questions wrong, can I get an explanation on how to use this function to solve this problem.

The function that relates the inverse of speed (1/5) (i.e., the time in minutes that it takes to travel 1 mile) to traffic (T) on a highway is 1/5 = 2 + 0.05T. Demand for traffic (measure as traffic volume per minute) on this road is 7 =3,100-70.(1/S). a. Find the equilibrium traffic volume in the absence of any congestion toll. b. Find the marginal cost function for traffic volume, where cost is expressed as travel time per mile in minutes. c. Find the optimal level of traffic volume. d. Find the optimal congestion toll, expressed in minutes. (Imagine that the congestion toll consists of sitting in the "penalty box" for this period of time.)