Hi experts

I am a newbie i want to know how you can subtract GF2 values one after the other .I have 4 new sub heading i need to create,for example
GF2.A-GF2.B = Gross profit
GF2.B-GF2.C = Operating profit
GF2.C-GF2.D = Profit before tax
GF2.D-GF2.E = Net profit
if this has been done before please include a link for me ,i need to same guidance

Regards