I don't know how to do it, but Wolfram Alpha is a computational search engine that tells you the answer to pretty much any math problem you have:
http://www.wolframalpha.com/input/?i=85+...25+seconds
Update:
Here's how you do it: http://www.ehow.com/how_2363249_form-dec...-form.html
http://www.wolframalpha.com/input/?i=85+...25+seconds
Update:
Here's how you do it: http://www.ehow.com/how_2363249_form-dec...-form.html