As dragonchild said this sounds a bit like homework and if it is it wouldn't be really fair to give you the answer :). But heres a hint.

If I understand you correctly you want to get rid of the SYMM part form the line. For that you probably want to use regular expressions. Look into the 's' (switch) operator. And follow dragonchild's suggestion on reversing the signs.

Hope that helps.
Chris

Update: That should be 's' for the substitution operator. I was still asleep when I wrote this :). (Thanks to premchai21 for pointing that out)