my %muthash = (
        "key1" => 1,
        "key15" => 3,
        "key150" => 1 );
my %copyhash = (
        "key1" => 1,
        "key15" => 1,
        "key140" => 1 );
my %mergedhash;
foreach (keys %muthash){
$mergedhash{$_} = $muthash{$_}+ $copyhash{$_};

}
foreach (keys %copyhash){
$mergedhash{$_} = $muthash{$_}+ $copyhash{$_} unless defined $mergedhash{$_};
}
print Dumper(\%mergedhash);