You want to borrow $a, with monthly payment of $p, such

that you'll owe $f after making n payments, at monthly rate r%.

Example:

Code:

```
MONTH PAYMENT INTEREST BALANCE
0 3000.00
1 -522.56 30.00 2507.44
2 -522.56 25.07 2009.95
3 -522.56 20.10 1507.49
4 -522.56 15.07 1000.00
```

Devise a formula calculating p in terms of a, f, n, r