String Search in PHP

Задание 1

Given a string:

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

Determine the position of the first letter 'b'.

Задание 2

Given a string:

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

Determine the position of the last letter 'b'.

Задание 3

Given a string:

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

Determine the position of the first found letter 'b', if you start the search not from the beginning of the string, but from position 3.

Задание 4

Given a string:

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

Determine the position of the second space.

Задание 5

Given a string:

php<?php
  $str = 'example..com';
?>

Check that the string has two dots in a row.

Задание 6

Given a string:

php<?php
  $str = 'http://example.com';
?>

Check that the string starts with 'http://'.