Counting Substrings in PHP

Задание 1

Given a string:

php<?php
  $str = 'aaa bbb ccc';
?>

Count the number of words in this string.

Задание 2

Given a string:

php<?php
  $str = 'hello hello world hello';
?>

Count how many times the substring 'hello' occurs in the string.

Задание 3

Given a string:

php<?php
  $str = '※※※';
?>

Count how many times the substring '※' occurs in the string.

Задание 4

Given a string:

php<?php
  $str = 'abracadabra';
?>

Count how many times each character appears in the string.

Задание 5

Given a string:

php<?php
  $str = 'The quick brown fox jumps over the lazy dog';
?>

Count the number of words longer than three characters.