Answer:
28 minutes
3.5 x 8 = 28
Explanation:
Feeding the whole school (8/8) would take 8 times as long as feeding 1/8 of the school.
3 1/2 can become 3.5 if that's easier for you to work with.
Feeding 1/8 of the school is 3.5 x 1 = 3.5
Feeding 2/8 of the school is 3.5 x 2 = 7
Feeding 8/8 of the school is 3.5 x 8 = 28
It takes 28 minutes to feed the whole school (8/8)