http://www.1728.org/logrithm.htm
That's a website that will help with logarithms that you can't do on a regular calculator.
Or if you use the calculator on this website, hit the [log] button and type 22 before the open parenthesis and the type 641 after the open parenthesis. I should look like this:
log22(641)
Then hit the equals button twice. ^_^
