Adding in Unix

I've been thinking and cannot figure out a way to add a column of numbers in a file when each number I want is in a seperate line. For example, let's say the information below is my file:

blah blah blah 456 324 554
blah blah blah 567 234 987
blah blah blah 456 324 534
blah blah blah 456 224 554
blah blah blah 456 344 554
blah blah blah 456 324 544
blah blah blah 456 325 554
blah blah blah 456 324 554

Ok, how would I add the fourth column in this file (first column of numbers)? I know how to sort from each column, and that's about all. So far, the man pages for sort, grep, wc, etc..., have not helped me. But, I don't know what other commands might help me better. Thanks for your help!

sort, grep, wc have nothing to do w/ your probl,
sed, ed, vi, awk, perl or c are the friends for this.
assumed the input is, like you say:
>>>>> blah blah blah 567 234 987
have a look what sed can:

sed 's/\(.*\) \(.*\) \(.*\) \(.*\) \(.*\) \(.*\) /\1 \2 \3 aaaa\4 \4bbbbb \5 \6/' input>output

try just for fun and read the manual pages
feel free to optimize the code
for filemanipulations not needing numerical computing or formating sed is the best.
AND the same syntax works in ed, vi, awk, perl got a modern one, but should also support that.
so learn once and reuse.

Try:
awk '{x+=$4} END{print x}' file

sorry, i did not understand: (numerical) add.
perderabo is OK.