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