Reversing Arrays in PHP

Задание 1

Given an array:

php<?php
  $arr = ['a' => 1, 'b' => 2, 'c' => 3];
?>

Swap the keys and values in it.

Задание 2

Given an array:

php<?php
  $arr = [1, 2, 3, 4, 5];
?>

Make the following array from it:

php<?php
  [5, 4, 3, 2, 1]
?>