A bank charges a service fee of $7.50 per month for a checking account. A bank account has $85.00. I

A bank charges a service fee of $7.50 per month for a checking account. A bank account has $85.00. If no money is deposited or withdrawn except the service charge, how many months until the account balance is negative?

Let m be the number of months. Our balance is denoted by B(m):
B(m) = 85 - 7.5m

The question asks when B(m) is less than 0. So we set up an inequality:
85 - 7.5m < 0

To solve this inequality for m, we type it in our search engine and we get:
m > 11.3333

We round up to the next whole integer and get m = 12