Which of the following expressions shows the number of 8 character passwords that can be formed using letters and digits if the password must begin with a letter?

26 x 36 x 36 x 36 x 36 x 36 x 36 x 36 
You may also see it written as 26 x (36)^7

To understand this expression, you must first know that they are 26 letters and 10 digits (1 through 9 and zero).

Now, to find the total number of possibilities, you simply multiply all of the options for each position in the password.

First, we must have a letter, so there are 26 options. Then, for the remaining 7 places, there are 36 options (26 letters and 10 digits).

The answers are 20,30,80,180,960,890,1230,4560. on the first row