i just want to how can we subtract the highlighted ones from the total.

eg:
1256 sdkjfs
1236 dfsdf
2569 dfsdfs
2669 dfsdfs
3214 dfsdf
2200 sdfsdf
1230 dfsdfsdf

when i highlight the 2nd column each time i want the 1st column to be
subtracted from the total(all the highlighted ones).

thank you