How to add sign to a cell based on data in another cell?

I would like to add sign to a Number cell based on whether the preceeding column contains the pop-up option 'Debit' or 'Credit'.

If 'Debit' is selected, the amount entered (number) should be converted to a negative number. If 'Credit' is selected, the number should remain as it is.

I know that in Numbers a cell can only be used to either store user-entered data or as a formula cell, i.e., it cannot do both.

So I created another column that will perform the formula for me while also copying the amount entered in the original 'Amount' cell. However, I don't think my solution is elegant.

I would like to know if there is a better way to do this, as I don't want to have two columns visible in my table.

Thanking you.