my math stinks

Hi All, This is the first time I have had to deal with math. I have gone through the manual and a few books and I think I am worse off then when I started. Can someone give me an example of the simple math below. I think If I see some in code I can move on from there. I need to find out if $pa > $pb or $pb > $pa then subtract smallest from the largest and add $ca and then add $ps TIA Gary