Shorthand Operations in PHP

Let's take the following code:

<?php
	$num = 1;
	$num = $num + 2;
?>

As you can see, the variable is assigned its current value plus something else. For such operations, there is a special shorthand operator +=, see the example:

<?php
	$num  = 1;
	$num += 3; // equivalent to $num = $num + 3;
?>

There are similar operators for other mathematical operations:

<?php
	$num  = 2;
	$num -= 3; // equivalent to $num = $num - 3;
?>

<?php
	$num  = 2;
	$num *= 3; // equivalent to $num = $num * 3;
?>

<?php
	$num  = 2;
	$num /= 3; // equivalent to $num = $num / 3;
?>

<?php
	$str  = 'a';
	$str .= 'b'; // equivalent to $str = $str . 'b';
?>

Simplify the provided code using shorthand operations:

<?php
	$num = 47;
	$num = $num + 7;
	$num = $num - 18;
	$num = $num * 10;
	$num = $num / 15;
	echo $num;
?>

Simplify the provided code using shorthand operations:

<?php
	$str = 'a';
	$str = $str . 'b';
	$str = $str . 'c';
	
	echo $str;
?>