foreach ($b as $state => $info)
{
  print_r($var[$state]);
}

-----
two different instances of $var
Array
(
    [a] => Array
        (
            [e_u] => Array
                (
                    [26] => 2
                    [27] => 2
                    [28] => 2
                )

        )

)

Array
(
    [d] => Array
        (
            [k_u] => Array
                (
                    [13] => 1
                    [12] => 1
                )

        )

)