So, after the nail set is bought, she will have 80-16 left, that is 64. If each pair of earrings costs 8 dollars, then she can buy 64/8 =8: She can buy 8 pairs of earrings.
I don't see how you can make an "inequality" with this.
If the question is interpreted that she doesn't spend all her money, then we could say, if we must that if y=number of earrings she can buy then
y≤8