compare then Strikethrough

Hi,
I am trying to compare Column A,B and C.
If it finds a duplicate row then it should put a Strikethrough into the cell in column C. The only other thing is that the cells in C column are not hundred percent the same. They have a positive number and a negative number of the same. Like "-5" and "+5". The reason why I would like to Strikethrough is because they cancel each other out.

Thanks a million
Andonny