Average Speed of a Vehicle The average speed of a vehicle on a stretch of Route 134 between 6 A.M. and 10 A.M. on a typical weekday is approximated by the function f(t) = 10t - 20vt + 30 (0 s t s 4) where f (t) is measured in miles per hour, and t is measured in hours, with t = 0 corresponding to 6 A.M. At what time of the morning commute is the traffic moving at the slowest rate? A.M. What is the average speed of a vehicle at that time? mph