Average Speed of a Highway Vehicle The average speed of a vehicle on a stretch of Route 134 between 5 a.m. and 9 a.m. on a typical weekday is approximated by the function f(t) = 30t - 60vt + 40 (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 5 a.m. Find the interval where f is increasing and the interval where fis decreasing. (Enter your answers using interval notation.) increasing calcPad + Operations decreasing Functions X Symbols