PHP Taskbook Level 3.10

Given an array, make each element in it repeat twice.

Given an array and a number, leave in the array only those numbers that are divisors of the given number.

Given two numbers, get an array of digits that are in both numbers.

Given a number, get an array with the position of all 3 digits in that number, excluding the first and last.

Given an array of numbers, leave the numbers in it that consist of different digits and delete the rest.

Given an array:

[
	[1, 2, 3],
	[4, 5, 6],
	[7, 8, 9],
]

Merge the elements of this array into one one-dimensional array:

[1, 2, 3, 4, 5, 6, 7, 8, 9]