求解数组序号及所在位置解决思路

$arr = array (
  0 => 
  array (
    0 => 'SU14031300617',
    'po_num' => 'SU14031300617',
  ),
  1 => 
  array (
    0 => 'SU14031300623',
    'po_num' => 'SU14031300623',
  ),
  2 => 
  array (
    0 => 'SU14031300626',
    'po_num' => 'SU14031300626',
  ),
  3 => 
  array (
    0 => 'SU14031300627',
    'po_num' => 'SU14031300627',
  ),
  4 => 
  array (
    0 => 'SU14031300616',
    'po_num' => 'SU14031300616',
  ),
  5 => 
  array (
    0 => 'SU14031300618',
    'po_num' => 'SU14031300618',
  ),
  6 => 
  array (
    0 => 'SU14031300622',
    'po_num' => 'SU14031300622',
  ),
  7 => 
  array (
    0 => 'SU14031300624',
    'po_num' => 'SU14031300624',
  ),
  8 => 
  array (
    0 => 'SU14031300625',
    'po_num' => 'SU14031300625',
  ),
)

foreach($arr as $k=>$tmp) {
    if('SU14031300617' == $tmp[0]) {
        return ($k+1) . '/' . count($arr);
    }
}
return false;