Getting array value by string key

Question

I have array and i nees access to key:

var_dump($load);

array (size=18)
  '4' => 
    array (size=3)
      0 => string '12.3%' (length=5)
      1 => string '17.8%' (length=5)
      2 => string '11.8%' (length=5)
  '9' => 
    array (size=3)
      0 => string '5.0%' (length=4)
      1 => string '8.2%' (length=4)
      2 => string '8.9%' (length=4)
  '24' => 
    array (size=3)
      0 => string '53.1%' (length=5)
      1 => string '86.1%' (length=5)
      2 => string '53.6%' (length=5)
  '7' => 
    array (size=3)
      0 => string '95.1%' (length=5)
      1 => string '90.1%' (length=5)
      2 => string '80.7%' (length=5)

Hove a can get data on key?

var_dump($load["7"]);
var_dump($load["'7'"]);
var_dump($load['"7"']);
var_dump($load[7]);

All var_dump return null;

Var dump array keys, Keys match.

$keys=array_keys($load); var_dump($keys);

array (size=18)
  0 => string '14' (length=2)
  1 => string '60' (length=2)
  2 => string '19' (length=2)
  3 => string '7' (length=1)
  4 => string '15' (length=2)
  5 => string '24' (length=2)
  6 => string '1' (length=1)
  7 => string '16' (length=2)
  8 => string '5' (length=1)
  9 => string '11' (length=2)
  10 => string '17' (length=2)
  11 => string '18' (length=2)
  12 => string '3' (length=1)
  13 => string '6' (length=1)
  14 => string '2' (length=1)
  15 => string '10' (length=2)
  16 => string '9' (length=1)
  17 => string '4' (length=1)