#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;
use List::Util qw/sum/;

my $aoa = [];
my $cur = [];

while (<DATA>) {
    chomp;
    push @$aoa, $cur and $cur = [] and next if /^$/;
    push @$cur, (split /\s/)[1]; # nur eine Spalte
}
push @$aoa, $cur;
print Dumper $aoa;

# mittel bilden

@$aoa = map { sum(@$_)/scalar(@$_) } @$aoa;
print Dumper $aoa;

__DATA__
12 15 17 13
22 35 11 14
10 25 19 14
32 18 27 25

33 13 13 26
16 42 29 13
61 11 22 14
52 31 17 25
18 14 27 39