Ten thousands’ place (10⁴) can be filled with 1 and 2 i.e. ten thousands’ place can be filled in 2 ways. [as, it cannot be filled with 0, because it will become a 4-digit number then]

From the thousands’ place (10³) to the ones’ (10⁰) place can be filled with 0 or 1 or 2, so, 4 places can be filled in 3 ways.

As, the operations are dependent, so, total number of ways

.

The discussion can be shown pictorially as: