Camille Harris has a checking account with the Bank of the NorthWest. She earns 0.5% per month. If she maintains a balance of $1200, her checks are free, but if she goes under that amount, each check will have a two cent charge on it. For balances under $600, there is a service fee of $4 per month. Use the equation I = rB - sx - f to determine her earnings on the account if she has a balance of $1500 and she writes 25 checks.
A.$3.00
B.$3.50
C.$7.00
D.$7.50