use Modern::Perl;

my %hash = (
    ABCDE => 12,
    FGHIJ => 7,
    KLMNO => 2
);

say getMatchResult( 'AC', 'ABCDE' );

sub getMatchResult {
    my ( $find, $key ) = @_;
    my $matches = () = $key =~ /[$find]/ig;

    ( $matches / 5 ) * $hash{$key};
}

##</code><code>##

4.8