In the same cell if your balance is 900 you enter =900 - 300 your result of
600 will appear in the same cell when you press enter.

If you use two cells for the function and a third for the result, assuming
col A:

enter 900 in A1 and 300 in A2, In A3 type =A1 - A2 and press enter your
result will be in A3

"Palliative" wrote:

How do you subtract from the bank balance like when you put -300 i want it to
subtract from the balance below