I need the formula to arrive at the following.

N is 85% of _____ (number)?

Sample:

I receive $145 from you. You tell me that this is my percentage, which we both know is 85% of the total number. You receive 15% of the total number.

What is the total number? What is your 15%? And what is the formula I use to arrive at these numbers? (I need it frequently, and I never remember it. I’m an idiot at math.)

I would be forever in your debt…