The distance x, in feet, between successive cars on a certain stretch of highway has the following probability density function, where k=1/a and a is the average distance, in feet, between successive cars over some period of time. f(x)=ke−kx, for 0≤x<∞ A transportation planner determines that the average distance between cars on a certain highway is 140 ft. What is the probability that the distance between two successive cars, chosen at random, is 30 ft or less?