Solution
= Solution
The <rule of product> counts $7^4$ unrestricted passwords and $6^4$ passwords containing no A. By the <rule of subtraction>, the answer is
$$
\boxed{7^4-6^4=2401-1296=1105.}
$$
= Solution
The <rule of product> counts $7^4$ unrestricted passwords and $6^4$ passwords containing no A. By the <rule of subtraction>, the answer is
$$
\boxed{7^4-6^4=2401-1296=1105.}
$$