Calculating Price Using Width, Length, and Quality

  <form action="http://www.cartserver.com/sc/cart.cgi" method="post">
    <img align="left" src="velvet.jpg"   alt="Image" />
    <input type="hidden" name="item" value="s-8882^ve-1^Antso Velvet Carpet^op1op12op5^op3^^^lin ft.^10^http://www.cartserver.com/sc/misc/velvet.jpg" />
    <!--Item fields are (from left to right):
    cart-id
    part number
    description
    cost
    quantity
    per item shipping fee (optional)
    per item insurance (optional)
    unit of measure (optional)
    shipping weight per unit (optional)
    link to picture (optional)
    --> 
    <strong>Antso Velvet Carpet</strong><br />
    <input type="hidden" name="op5" value=" - $8.00" />
    <!--base price per linear foot-->
    <select name="op1">
      <option value="=error= You must select either 12' or 15' roll width"> Select Width </option>
      <option value="12' - $0.00"> 12' (base price) </option>
      <option value="15' - $2.25"> 15' (add $2.25/lin ft) </option>
    </select>
    <br />
    <select name="op12">
      <option value="=error= You must select 1/4, 1/2, or 5/8 in. pile depth"> Select Pile Depth </option>
      <option value="1/4 in pile - $0.00"> 1/4 in. pile (base price) </option>
      <option value="1/2 in pile - $1.00"> 1/2 in. pile (add $1.00/lin ft.) </option>
      <option value="5/8 in pile - $1.50"> 5/8 in. pile (add $1.50/lin ft.) </option>
    </select>
    <br />
    <select name="op8">
      <option value="=error= You must choose a carpet color."> Select Color </option>
      <option value="Color:PG"> Pine Bough Green </option>
      <option value="Color:CR"> Crimson Tide </option>
      <option value="Color:MB"> Midnight Blue </option>
      <option value="Color:TS"> Tequila Sunrise </option>
    </select>
    <br />
    Enter Linear Feet:
    <input type="text"  name="op3" value="0" />
    <br />
    <input align="center" type="image" border="0" name="add" src="/images/addtocart.gif" />
    <div style="clear:both"></div>
    This style carpet sells at $8.00 per linear foot. Some options are extra.
    <p></p>
  </form>