logic to actually sum all the cvalues arising of a difference across the row

I need to have a logic to actually sum all the values arising of a difference across the row..

For ex:-
i have given a piece of work to different people and i want to check how many times they have reverted back to me..

Col A Col B Col C Col D
1st Query 1st Revert 2nd Query 2nd Revert Total
11-Sep-07 12-Sep-07 13-Sep-07 15-Sep-07 3

What i want is to minus (revert from query) and add all the days across the row..
like 12-Sep-07 - 11-Sep-07 = 1 , 15-Sep-07 - 13-Sep-07 = 2
and add the difference across the rows. 1+ 2 =3

As good as writing= sum(h2-g2,j2-2,...so on..)

but i will be having more columns and that is not going to be fixed

so is it possible to have a logic to get the answer?.