&lt;?php    function calc&#40;$price, $tax=&quot;&quot;&#41;    &#123;        $total = $price + &#40;$price * $tax&#41;;        echo &quot;$total&quot;;     &#125;    calc&#40;42&#41;;        ?&gt;
A. Error
B. 0
C. 42
D. 84
Answer:A
&lt;?php    function calc&#40;$price, $tax=&quot;&quot;&#41;    &#123;        $total = $price + &#40;$price * $tax&#41;;        echo &quot;$total&quot;;     &#125;    calc&#40;42&#41;;        ?&gt;
A. Error B. 0 C. 42 D. 84
Explanation: You can designate certain arguments as optional by placing them at the end of the list and assigning them a default value of nothing.