Answer: +24.
Step-by-step explanation:
Given : You are swimming each 25 yd length of a swimming pool 3 seconds faster than your personal best.
i.e. for each 25 yd length of a swimming round, +3 seconds faster than your personal best.
If the swimming timing is 200 yards, then the number of 25 yd length round of swimming in it :-

Then, the change in time of your personal best after 200 yards :-

Hence, the integer represents your change in time of your personal best after 200 yards = +24.