The first digit of the password can be any of the ten digits - 10 possibilities.
A digit cannot be repeated, so the second digit can be any digit except the one you chose for the first digit - 9 possibilities.
The third digit can be any digit except the digits you chose for the first and second digit - 8 possibilities.
Using the rule of product:

There are 720 passwords.
Answer:
It's a.
Step-by-step explanation:
(a - 2b)^2 + 8ab
= a^2 - 4ab + 4b^2 + 8ab
= a^2 + 4ab + 4b^2.
((a + 2b)^2 = a^2 + 4ab + 4b^2.