in reply to Not sure if possible?

I was going to mention CGI Redirect, but thats way more than what you need.
For this script just add a simple link back to the starting script. 

<a href="Calculator.html" target="_self">Back to Calculator</a>

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If you want it to look like a button there are a few CSS and other HTML tags that can be used to give the effect and its easy to add a CSS class to the link above.
Update: to add the link in the quotes you have in print you will need to escape the links quotes \"\". 
print "<a href=\"Calculator.html\" target=\"_self\">Back to Calculator
+</a>";

[download]
Or I would just wright it like this. 
    print <<"HTML";
Content-type:text/html

<html>
<head>
<title> Answer Page</title>
</head>
<body>
<p>
<h2> The answer to your calculation is: $answ </h2><br />
<a href="Calculator.html" target="_self">Back to Calculator</a>
</p>    
</body>
</html>
HTML

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