MENGHITUNG LUAS & VOLUME TABUNG PHP

<?php
$r = 20;
$t = 56;
$phi = 22/7;
$v = $phi * $r * $r * $t;
$l1 = 2 * $phi * ($t + $r);
$l2 = 2 * $phi * $r * $t;

echo "MENGHITUNG LUAS & VOLUME TABUNG <br>";
echo "==================================<br><br>";
echo "Jari-Jari = $r <br>";
echo "Tinggi = $t <br>";
echo "maka : <br>";
echo "<li> Volume tabung = $v </li>";
echo "<li> Luas permukaan tabung = $l1 </li>";
echo "<li> Luas selimut tabung = $l2 </li><br><br>";

?>