The store buys the bikes that they sell for $35, and they sell them for $85, so in order to find the actual amount of money earned from one sale, you have to subtract how much they sell the bikes for by how much they bought them for, so:
85 - 35 = 50
Then, you divide the $3250 by the 50:
3250 / 50 = 65
So now we know that the store must sell 65 bikes a month to break even.
