Since you know what needs to be sent and it doesn't necessarily jive with the form, you're better off bypassing the normal form logic by calling ->get or ->post directly. (->post is inherited from LWP::UserAgent.)

$mech->post(
   $uri,
   [
      ...,
      email => 'samba@gmail.com',
      samba => '45',
      samba => '172',
      samba => '39',
   ],
);
[download]

If the list of numbers isn't constant, the following might be more useful:

my @sambas = ('45', 172', '39');

$mech->post(
   $uri,
   [
      ...,
      email => 'samba@gmail.com',
      ( map { samba => $_ } @sambas ),
   ],
);
[download]