php acting like text.

My php code is not being treated like code. 

This line in my html     <input type='text' name='k' size='70' value='<?php echo $_get['k']; ?>' />

Returns an input field with the text    <?php echo $_get[    inside of it.

The   '<?php echo $_get['k']; ?>'  is supposed to return the result of a php echo function to put the text typed into the box back into the box after the Search button is pressed.

I have installed MAMP and created a "localhost" with my site on it.