Formula to determine principal pay down

[elisaleach]

I need a formula to determine the amount of principal i have to pay down in order to get a loan back into compliance. need to set up and forecast what the pay down would have to be in the future as well.
For example, i need 1.10 coverage which i miss by $150,000. With a current principal balance of $17,000,000 on a 7% 25 yr am, what formula can i set up?
Thanks

 

[Niek84]

I'm not entirely sure what you're trying to achieve, but it looks to me like you could use the solver function