What is method to add PHP code into a text block or HTML object?

The code:

-------------------

<?php

// add sample PHP code here

$data1 = 35;

$data2 = 2;

$result = $data1 + $data2;

echo "Calculated value = ".$result;

?>

-------------------

does not work in text box with HTML enabled or in the HTML object.

The custome PHP code would make calculations or look up values dynamically.

Any ideas?