Case 1
forming 4 digit number,
When 7 is at 1000′s place
7___,
So total number of ways will be 4×3×2=24 ways,
Case 2
forming 4 digit number when 8 is at 1000′s place
8___,
So total number of ways will be 4×3×2=24 ways,
Case 3
forming 5 digit number,
So total number of ways will be 5!=120 ways,
Now adding all the cases we get, 120+24+24=168 ways.