Need help with game logic

So, I’ve been working on a basic gym simulator game as a small project to learn how to script, But I need help balancing earning in-game currency, Here’s the current math:

player.leaderstats.Cardio.Value = player.leaderstats.Cardio.Value +strength / 50

Can’t for the life of me find a way to balance this, Please help.

What are the currencies, what do you buy, what do you sell?

You gain cardio via a treadmill
You gain strength via a weight
You use cardio to unlock certain weights (First weight to buy costs: 100 Cardio) You gain cardio via a treadmill, you start with “0.5” cardio, you gain a low amount of cardio via using weights, to get players started, players need 50 strength to use the treadmill. The problem is that the players are gaining too much cardio, meaning that I have to make the cardio price to be in the billions for the 4th item.

Maybe reduce cardio then. Depending on how much you want the cardio cap to be.