I am not sure how to tackle this problem. Could one explain how to do this the long way (like finding all the interests and subtracting) and how to do it with a formula. I just want to learn how to do this.

"Robyn borrows $10000 from a bank. Interest at 18% per annum is calculated monthly on the amount of money still owing. Robyn repays $600 each month. How much does Robyn owe the bank after the first 12 repayments?"

I am not sure if one should first find the interest and then subtract 600 or the other way around. And then where to go from this. If anyone can help me grab the idea behind this finance problems it will really be helpful.

Month Carried Fwd Interest Reypayment

1 10000 150 600

2 9550 143.25 600

3 9093.25 136.39875 600

4 8629.64875 129.4447313 600

5 8159.093481 122.3864022 600

6 7681.479883 115.2221983 600

7 7196.702082 107.9505312 600

8 6704.652613 100.5697892 600

9 6205.222402 93.07833603 600

10 5698.300738 85.47451107 600

11 5183.775249 77.75662874 600

12 4661.531878 69.92297817 600

4131.454856

After the 12th month's payment he owes $4131.45