Answer:
8 days late; C, division to find equal groups.
Explanation:
In order to find how many days, we must divide 80 by 10 to find how many groups of 10, aka, how many days, there are.
80/10 = 8
This means her book was 8 days late.
You're dividing to find equal groups because you need to find equal groups of ten cents to determine the number of days.