Question 430898
How many letters are there ? And does case matter?
If you say there are 26 letters and 10 digits, then the result is as follows.
You have 26 choices for the first letter, 26 for the second and 26 for the third.
Your have 10 choices for each of the remaining 4 positions
So
{{{26 * 26 * 26 * 10 * 10 *10 * 10}}}
You can take it from there

If you can have lower case letter, or allow special charactiers (like space or $ or whatever) then just bump up the number accordingly and do the math again.

Make sense?