Assuming that it's a normal racetrack, and each pair had to run 1 lap, they should have to run about 400m (roughly 1/4 mile).
We can also see on the first page that the teams are lined up in the middle of the straightaway,
so when they are rounding the last corner there is only 25m left, as stated.
We also saw that when Hanako fell, Saotome was rounding the first corner.
Therefore Hanako ran 375m in the time it took Saotome to run 350m.
This is very believable, but conveyed very poorly as the distance was covered in like a page.