Александр

<?php

$a = [
	1,
	3,
	6
];

$b = [
	[
		'Simple String 0'
	],
	[
		'Simple String 1'
	],
	[
		'Simple String 2'
	],
	[
		'Simple String 3'
	],
	[
		'Simple String 4'
	],
	[
		'Simple String 5'
	],
	[
		'Simple String 6'
	],
	[
		'Simple String 7'
	],
	[
		'Simple String 8'
	]
];

$c = [];
foreach($b as $index => $item) if(in_array($index, $a)) $c[] = $item;

var_dump($c);
/* array(3) {
  [0]=>
  array(1) {
    [0]=>
    string(15) "Simple String 1"
  }
  [1]=>
  array(1) {
    [0]=>
    string(15) "Simple String 3"
  }
  [2]=>
  array(1) {
    [0]=>
    string(15) "Simple String 6"
  }
} */