use List::Util qw[ sum ];
...
sub subroutine {
    our( @a, @b, @c, @d, @e );
    ( *a, *b, *c, *d, *e ) = @_;

    foreach my $i ( 10 .. $#a ) {
        $c[$i] = $d[$i] = $e[$i] = 0;
        my $b = $b[$i];
        if( ( $b >= 5 ) && ( $b < 7 ) ) {
            $c[$i] += sum @a[ $i-$b+1 .. $i ];
            $c[$i] /= $b;
        }
        elsif( ( $b >= 7 ) && ( $b < 9 ) ) {
            $d[$i] += sum @a[ $i-$b+1 .. $i ];
            $d[$i] /= $b;
        }
        elsif( ( $b >= 9 ) && ( $b < 15 ) ) {
            $e[$i] += sum @a[ $i-$b+1 .. $i ];
            $e[$i] /= $b;
        }
    }
    return;
}

## called like this
my @a = ...;
my @b = ...;
my( @c, @d, @e );
subroutine( \@a, \@b, \@c, \@d, \@e );