Add and find the rank in array using php

Hi 
Recently i went to interview i was asked to add a mark and find the rank of it using php.

1) First i created a function called rankChecker and passing  two parameter like collection of marks in array and mark that will be added and finding the rank of it.
2) Then i created dumpy variable $s ,$ab as array.
3)After that i added the mark in the array mark list and sorted into descending order and looped in for loop.
4) passing the value of first array into dumpy array $ab as key and passing the $i value  incremented by one as $i starts with zero.
5) And returning the current $ab array and passing $mark as key value in it.


function rankChecker($arr,$mark){
$arr[] = $mark;
rsort($arr);
$ab = array();
//echo count($arr);
   for($i=0;$i<count($arr);$i++){
        $ab[$arr[$i]] = $i+1;
      }
return $ab[$mark];
}

$arr=[39,37,34,56,67,23,37];
$mark=10;
print_r(rankChecker($arr,$mark));