Answer:

We can have either 4 digit or 5 digit number.

First consider 4 digit number.

We can take 6,7,8 at the thousandth place.

The next three places can be filled in

4

C

3

⋅3! way.

So we get 72 such numbers

For 5 digit number, we can choose them in 5! ways(120).

So total no of such numbers are 72+120=192.