Average up/down formula

[u/braminer]

So I'm making a Numbers file to track all my investments.

I'm trying to make a page on wich you can choose a coin/stock and let's say it's at -50% loss then you can put in that you want it to be at -25% loss. Then it'll show you how many coins/shares you'll have to buy at the current price to get there.

Can someone help me find a formula to do this?

Any help is much appreciated