I have Mod2.pm:

#!/usr/bin/perl -w

package Mod2;

use strict;
use warnings;
use Mod3;

require Exporter;

our $VERSION = '0.1000';
our @ISA = qw/Exporter/;
our @EXPORT_OK = qw (double sixtimes);

sub double { return 2 *shift}
sub sixtimes {
    my $val = double shift;
    return Mod3::triple($val);
}
[download]

#!/usr/bin/perl -w

package Mod3;

use strict;
use warnings;
use Mod2;

require Exporter;

our $VERSION = '0.1000';
our @ISA = qw/Exporter/;
our @EXPORT_OK = qw (triple fourtimes);

sub triple { return 3 * shift}
sub fourtimes {
    my $val = Mod2::double(shift);
    return Mod2::double($val);
}
[download]

#!/usr/bin/perl

use feature qw /say/;
use strict;
use warnings;
use Mod2 qw /sixtimes/;
use Mod3 qw /triple fourtimes/;

for my $x (0..4) {
    say "$x * 3 = ", triple($x);
    say "$x * 6 = ", sixtimes($x);
    say "$x * 4 = ", fourtimes($x);
    say "$x * 6 * 4 = ", sixtimes (fourtimes($x));
}
[download]

$ perl usemod.pl
0 * 3 = 0
0 * 6 = 0
0 * 4 = 0
0 * 6 * 4 = 0
1 * 3 = 3
1 * 6 = 6
1 * 4 = 4
1 * 6 * 4 = 24
2 * 3 = 6
2 * 6 = 12
2 * 4 = 8
2 * 6 * 4 = 48
3 * 3 = 9
3 * 6 = 18
3 * 4 = 12
3 * 6 * 4 = 72
4 * 3 = 12
4 * 6 = 24
4 * 4 = 16
4 * 6 * 4 = 96
[download]

Or did I miss something in your question?