Looking for a way to calculate items needed to reach target %

GeneralDisarray had the right idea for what I was going for, just can't seem to find a way to turn that formula into something I can use as the numbers change.

Haseeb, what you suggested is the big issue I have been running into. Using the 100 calls, 15 sales, 20%goal example; That formula tells me you would need 5 more sales, which is not accurate b/c it does not factor in that 5 more sales would mean 5 more calls. So while 20/100 is 20%, 20/105 is only 19% and thus not at goal.

So in a nutshell, I have been trying to find a way to incorporate GD's formula. If anyone has any ideas I'd love to hear them or if I figure it out. I'll post and let you all know.