Password consists of upper

$-$

case letter, lower

$-$

case letter and digits.

If a password must contain at least

$1$

$$upper

$-$

case letter,

$1$

$$lower

$-$

case letter and

$1$

$$digit$,$ how many cases can be used if the password length is

a

$)$

$8$

b

$)$

$9$

c

$)$

$1$

$0$