Automate the Snipplr spambot protection

<?
 
$q = "What does seven * eight equal?";
 
 
$word_numbers = array("one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen");
$numbers = array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13);
 
$q = str_ireplace($word_numbers, $numbers, $q);
 
$word_signs = array("plus", "minus", "times", "x", "divided");
$signs = array("+", "-", "*", "*", "/");
 
$q = str_ireplace($word_signs, $signs, $q);
 
preg_match("!(\d{1,3}) ([^~]*?) (\d{1,3})!", $q, $out);
 
$first_number = $out[1];
$second_number = $out[3];
 
switch($out[2]) {
	case '+' :
		$answer = $first_number+$second_number;
	break;
 
	case '-' :
		$answer = $first_number-$second_number;
	break;
 
	case '*' :
		$answer = $first_number*$second_number;
	break;
 
	case '/' :
		$answer = $first_number/$second_number;
	break;
 
	default : 
		$answer = "Failed";
	break;	
}
 
echo $answer;
 
?>