In a race of 300 metres A beats B by 15 metres or 5 seconds. How much time A does take to complete the race?

From the question it is clear that speed of B = 15 / 5 = 3 m/s
The time taken by B to cover 300 m = 300 / 3 = 100 sec.
Hence, time taken by A to complete the race = 100 – 5 = 95 sec.