I have a formula that I use to balance my check book. If column D of the
current row (row of the current selected cell) is not 'P', It takes the value
in column G of the previous row, subtracts the value in column E of the
current row, adds the value in cell F in the current row and populates it
into column G of the current row. If column D of the current row (row of the
current selected cell) IS 'P', then column G of the current row is equal to
column G of the previous row.

Currently, I copy and paste the formula from cell (G,n-1) to cell (G,n). How
can I make this into a function?