<?php

$var1 = '3006';
$var2 = '40416';
$var3 = '966';
$var4 = '30';
$str = '$var1 + ($var2-$var3) / $var4.<br>';

eval ("echo $var1 + ($var2-$var3) / $var4;");


?>

$expression = "3006 + (40416-966) / 30";
eval('$result = '.$expression.';');