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 $600 and he writes 50 checks.