four race cars are traveling on a 2.5-mile tri-oval track. the four cars are traveling at constant speed of 195 mi/h, 190 mi/h,185mi/h, and 180 mi/h, respectively. assume you are an observer standing at a point on the track for a period of 30 minutes and are recording the instantaneous speed of each vehicle as it crosses your point. what is the time-mean speed and space-mean speed for these vehicles for this time period?