If Jif is 25th in line then that means there are 24 people in front of him

Jan has 124 in front of her.

Jan and Jif do not count as for people between them

So Between them is:

124 Infront of Jan

Minus 25 (Sing Jif does not count as he is the end)

So the answer is 99

But in reality in a College/highschool Canteen there would be an ever changing number of people/things(Kids can be odd).