How to define a function in PHP?

Type Hinting was introduced in which version of PHP?

Which type of function call is used in line 8 in the following PHP code?

 <?php
    function calc($price, $tax)	
    {
        $total = $price + $tax;
    }
    $pricetag = 15;
    $taxtag = 3;
    calc($pricetag, $taxtag);	
    ?>

 What will be the output of the following PHP code?

 <?php
    function calc($price, $tax="")
    {
        $total = $price + ($price * $tax);
        echo "$total"; 
    }
    calc(42);	
    ?>

Which of the following are valid function names?

i) function()
ii) €()
iii) .function()
iv) $function()

Which of the following are valid function names?

i) function()
ii) €()
iii) .function()
iv) $function()

What will be the output of the following PHP code?

<?php
    function a()
    {
        function b()
        {
            echo 'I am b';
 	}
        echo 'I am a';
    }
    a();
    a();
    ?>

What will be the output of the following PHP code?

  <?php
    function a()  
    {
        function b()
        {
            echo 'I am b';
 	}
        echo 'I am a';
    }
    b();
    a();
    ?>

What will be the output of the following PHP code?

<?php
    $op2 = "blabla";
    function foo($op1)
    {
        echo $op1;
        echo $op2;
    }
    foo("hello");
    ?>

A function in PHP which starts with __ (double underscore) is known as __________