Your netID password must be between 12 and 30 characters long and can include upper case letters, lower case letters, and digits. (There are a few other characters, but we'll ignore them for now.) One...

Your netID password must be between 12 and 30 characters long and can include upper case letters, lower case letters, and digits. (There are a few other characters, but we'll ignore them for now.) One way to measure how secure a password is would be to work out how long it would take to try all the possible passwords.  Choose a length (between 12 and 30) and assume that a hacker could try 15 passwords/second.  Calculate how long it would take to try all the passwords of that length, with reasonable units - that'll most likely be years.  You'll need to use the multiplication principle and unit conversions to get there.  Does it seem that this is long enough to be secure?