How to add PHP Calculation to Page

I am trying to add a page to my wordpress site that allows users to add in price and shipping options and then calculate the total cost. It works fine on the server outside of wordpress but when I add it to wordpress, I get a 404 error. What am I missing here? I’ve added PHP Execution but still it doesn’t work. Here is the code I’m using

<!– Script 4.1 – calculator.html –>
<div><p>Fill out this form to calculate the total cost:</p>

<form action=”handle_calc.php” method=”post”>

<p>Price: <input type=”text” name=”price” size=”5″ /></p>

<p>Quantity: <input type=”text” name=”quantity” size=”5″ /></p>

<p>Discount: <input type=”text” name=”discount” size=”5″ /></p>

<p>Tax: <input type=”text” name=”tax” size=”3″ /> (%)</p>

<p>Shipping method: <select name=”shipping”>
<option value=”5.00″>Slow and steady</option>
<option value=”8.95″>Put a move on it.</option>
<option value=”19.36″>I need it yesterday!</option>
</select></p>

<p>Number of payments to make: <input type=”text” name=”payments” size=”3″ /></p>

<input type=”submit” name=”submit” value=”Calculate!” />

</form>

</div>