How to find difference of two row values and store it as third row in the same table?

Hi,
   I want to find difference betwee two rows of a table and insert the difference value as third row in the same table. If the first row value is less than second row then the difference should appear within parenthesis instead of negative symbol.

Ex:
Name        Service1   Service2    Service3  Service4
xxx             98             70               50            85
yyy            50            90                35   &nbs ...