use strict;
use Data::Dumper;

my %h1 = (a => 1, b => 2, c => 3);
my %h2 = (a => 6, b => 8, c => 0);

my %h3 = map {$_ => $h1{$_} + $h2{$_}} keys %h1;

print Dumper \%h3;