Answer : 2. "7.5 min"
Explanation :

Answer: B) 7.5 min Explanation: B runs around the track in 10 min.  i.e ,    Speed of B = 10 min per round  Therefore,  A beats B by 1 round   Time taken  by A to complete 4 rounds    = Time taken by B to complete 3 rounds    = 30 min    Therefore, A's speed = 30/4 min per round = 7.5 min per round  Hence, if the race is only of one round A's time over the course = 7 min 30 sec