debt payments
posted by carol .
if I owe $5320.00 and must pay $300.00 a month plus 6% interest per annum till paid at approximately 18 months, how much interest money do I add to the $300.00 monthly payment

The question is confusing. If you pay $300 principal each month plus interest, the amount of interest will change each month. No reputable lender would charge interest on the original an=mount as the outstanding balance decreases.
I looked for a formula using constant principal payments, but could not fine one easily. So, an amortization schedule to fit the problem as posed would look like the chart below, where each line lists the payment number, the principal, interest, and remaining balance.
1: 300.00 26.60 5020.00
2: 300.00 25.10 4720.00
3: 300.00 23.60 4420.00
4: 300.00 22.10 4120.00
5: 300.00 20.60 3820.00
6: 300.00 19.10 3520.00
7: 300.00 17.60 3220.00
8: 300.00 16.10 2920.00
9: 300.00 14.60 2620.00
10: 300.00 13.10 2320.00
11: 300.00 11.60 2020.00
12: 300.00 10.10 1720.00
13: 300.00 8.60 1420.00
14: 300.00 7.10 1120.00
15: 300.00 5.60 820.00
16: 300.00 4.10 520.00
17: 300.00 2.60 220.00
18: 220.00 1.10