There are probably nicer ways to solve this, but this seems to work ;)

$a = "word 15,000 word word 20,000";
@b = split " ", $a;

$b[1] =~ s/,//g;
$b[4] =~ s/,//g;
print $b[1] + $b[4]."\n";
[download]

This will result in "35000"

HTH

Update: It'd of course be nicer (even in my messy example) to use a sub routine for this, which returns the commaless values ...