Suppose the number of laps = m
According to the question, each lap of 25 yards is covered 3 seconds faster than the previous one, so the series become
x , x-3 , x-6 , x-9, ............................
25 * m = 200
m =
m = 8
As m is the number of laps, and each lap is 3 second faster.
So 8 laps will be 8*3 = 24 seconds faster.