Answer:
assuming 30 day months:
Leonardo can pay up to $110 per month
credit card
daily interest = 14.5% / 360 = 0.040278%
monthly interest = (1 + 0.040278%)³⁰ - 1 = 1.2154%
I prepared an amortization schedule using an excel spreadsheet
It will take Leonardo 29 months to completely pay off his debt. The last payment will only be $37. Leonardo will be able to save $65 on his last payment if he uses his credit card.
store credit
daily interest = 19.3% / 360 = 0.05361%
monthly interest = (1 + 0.05361%)³⁰ - 1 = 1.6209%
principal will be $100 lower, $2,523.95
I prepared an amortization schedule using an excel spreadsheet
It will also take Leonardo 29 months to completely pay off his debt, but the last payment will be $102, which is higher than the $37 that he would need to pay using a credit card.