Napril 1974, steve prefontaine completed a 10-km race in a time of 27 min, 43.6 s. suppose \"pre\" was at the 7.15-km mark at a time of 25.0 min. if he accelerates for 60 s and maintains the increased speed for the duration of the race, calculate the acceleration that he had. assume his instantaneous speed at the 7.15-km mark was the same as his overall average speed up to that time.