Answer:
10 shelves
Explanation:
In order to calculate how many whole shelves we can fill we simply need to divide the total number of cereal boxes that John has in the back by the number of boxes that each shelf can hold like so...
85 / 8 = 10.625
Based on these numbers we can see that with the number of cereal boxes available we can fill a total of 10 shelves by using
10 * 8 = 80 cereal boxes
80 cereal boxes. That would leave 5 cereal boxes left which is not enough to fill another shelve.