Javascript calculation of remaining debt

[mlundqvist86]

I need help!

I have tried for a couple of Days now but can´t get it right.

I want to add calculation script that calculates a debt.

Example;

Total debt: 20 000 $

My debt: 10 000$

Girlfriends debt: 10 000$

Monthly pay off: 500$

I want a calculation that calculate remaining debt of the inidvidual and the total amount depending on the monthly pay off. Can somebody help?

/ Martin