Especially this part: [google.com...]
Look for: estimatedTotalResultsCount and estimateIsExact
As for how to use those two variables, you can store them, use them for calculations, or print them out to the screen or a web page or whatever you want.
For examples, there's an O'Reilly book called "Google Hacks" with a few examples online, and there's also the newsgroup google.public.web-apis [groups.google.com]
In a thread in that group, i found this syntax example for you:
my $results = $googleSearch -> doGoogleSearch($key, $query, $offset,
10, "false", "", "false", "", "latin1", "latin1");
print "About $results->{'estimatedTotalResultsCount'} results.\n";