Subnet Id of 8th subnet :- 192.168.10. 0111 0000
Broad cast Id of 8th Subnet : 192.168.10. 0111 1111
Last useful ip address for E0 router Interface will be : 192.168.10. 0111 1110 ---->192.126.10.126
So Option D is Correct .
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Edit :
They have mentioned that 0th subnet will not be a valid subnet so we start from 1
Subnet Id of 8th subnet :- 192.168.10. 1000 0000 (first 4 digit for subnet )
Broad cast Id of 8th Subnet : 192.168.10. 1000 1111
Last useful ip address for E0 router Interface will be : 192.168.10. 1000 1110 ---->192.126.10.142
Option A is correct.