I am trying to make a formula from known results that I have, but as I did basic maths at school I have no idea where to start. I had 2 tables, the first one was similar to:

.............8%
5%.......0.625
7.5%....0.938
10%.....1.250
The resulting formula here was easy, the percentage on the side divided by the 8%, which gave the results above, eg 5%/8% = 0.625. However, table 2 is far more complex, and way over my head:

.............8%
5%.......0.429
7.5%....0.890
10%.....1.494
12.5%...2.233
15%......3.100
17.5%...4.092
20%......5.203

I was asked to find out what would happen to our subsidiary company if the 8% fell to 7%.

Im good with excel, and want to make up a calc sheet to find out the answer, but previously I used our internal software to get info, and it only goes as low as 8%, and the company that made our company software went belly up, and no one here knows the formula that gave the original results.

Any help appreciated.