Answer:
n/5 and 1800 nails
Explanation:
The algebraic expression n/10, where n is the number of boards, represents the number of times he gets 2 free boxes of nails. So 2(n/10), or n/5, is the number of boxes, and 100(n/5), or 20n, is the number of nails. Substituting 90 in for n, Peter will get 1,800 nails.