Question

Alonzo Kelly has a checking account with the Central Bank. He earns 0.7% per month. If he maintains a balance of $1000, his checks are free, but if he goes under that amount, each check will have a three cent charge on it. For balances under $500, there is a service fee of $5 per month. Use the equation I = rB - sx - f to determine his earnings on the account if he has a balance of $900 and he writes 50 checks.