Question: in april 1974 steve prefontaine completed a 10 km race...

In April 1974, Steve Prefontaine completed a 10 km race in a time of 27 min, 43.6 s. Suppose "Pre" was at the 8.27 km mark at a time of 25.0 min. If he accelerated for 60 s and then maintained his increased speed for the remainder of the race, calculate his acceleration over the 60 s interval. Assume his instantaneous speed at the 8.27 km mark was the same as his overall average speed up to that time.

Please explain, I have gotten many answers and its been wrong every time.