u/Upstairs-Yak-5474

So I want an app or way so when someone buys a pack it subtracts from the case as well so for example.

Let's say we have

1 case = 10 packs

And we have 10 cases

If someone buys 10 packs I want the case to reduce to 9 and if I add ten packs I want the case to add to 11.

I really need advice, thanks for the help