Php Imprimir si un numero es par

<?php

/**
 * function to sum two numbers
 * @param integer $number_one  First number to sum
 * @param integer $number_two  Second number to sum
 * @return $total
 */ 
function addNumbers($number_one, $number_two) {
  $total = 0;
  // sum a plus b
  $total = $a+$b;
  // return the sum 
  return $total;
}

//example
$result = addNumbers(1, 2);

//output
echo $result; //3