my $req = POST(
    "http://myurl/public_html/cgi-bin/json-addition.cgi",
    Content_Type => 'application/json',
    Content      => $json->encode($data),
);

my $response = $ua->request($req);
$response->is_success or die($response->status_line);

my $result = $json->decode($response->decoded_content);
print $result->{c}, "\n";