A website instructs users to create a password using 4​ alphanumeric characters (letters or digits). Capitalization doesn't matter. How many such passwords are possible that do not repeat any characters?

A bicycle wheel rotates 400 times per minute. If the rider removes his feet from the pedals, the wheel will start to slow down. Each minute, it will rotate only as many times as in the preceding minute. How many 4 times will the wheel rotate in the eighth minute after the rider's feet are removed from the pedals? The wheel will rotate about times in the eighth minute. (Round to the nearest integer as needed.)