This works much the same in PHP as any other language. Paste this into firstphppage.php to add to the existing PHP lines:
$firstvalue=4;
$secondvalue=7;
$total=$firstvalue+$secondvalue;
echo "<p>The total is {$total}</p>";
You should easily see how to subtract by changing one character in that code. The multiply operator is *. The divide operator is /. Replace the + with these in the page and test the results.
