I need to change positive values to negatives

I have a worksheet containing many lines of data. Columns K, L, and N contain numerical values. What I need to happen is:

Look at the value in column K, if it is a negative value, convert the values in column L and column N to a negative value. For instance:

K value -1241.30
L Value 778.00. Need to change this to -778.00.
N Value 778.00. Need to change this to -778.00



I could do this by adding columns and using IF/THEN statements, but I suspect that a fairly simple macro could do this better.
I will attach a sample file
I appreciate any assistance.
Lance

Seems to work for me also,
Thanks for the help