in order to calculate how many rings does he have to sell to break even we first have to calculate the profit that he has on the sell of every ring from which he can take money to pay per supplies, so that would be the selling price minues expenses:
8-1.5=6.5
Now we have to divide the 91 in supplies by the profit:
91/6.5=14
So he has to sell 14 rings in order to break even between expenses and supplies.
