#!/usr/bin/perl

use strict;
use warnings;

my (@left, @right);

while(<DATA>) {
    chomp;
    my ($left, $right) = split /,/;
    push(@left, $left);
    push(@right, $right);
}

@left = sort { $a <=> $b } @left;
@right = sort { $a <=> $b } @right;

print "$left[$_],$right[$_]\n" for 0 .. $#left;

__DATA__
10,20 
30,10 
20,70 
70,80 
40,90 
90,100 
50,50