1) First Group = 128 customer , per customers 256 address ,
so for 256 address , we need 8 bits (for host)
host contain = 8 bits and 32-8= 24 for NID ,
so for group 1 st 128*256(per customer) = 32768 address ,
it will be like
145.75.0.0/24 to 145.75.0.255/24 for 1st customer(as each customer have 256 address)
145.75.1.0/24 to 145.75.1.255/24 for 2nd customer ..
....
145 .75.127.0/24 to 145.75.127.255/24 for 128th customer
now group 2 64 address so need 6 bit for host and remaining are 26 bits
so total address for it 64*128 =8192
address like 147. 75.128.0/26 to 147.75.128. 63 /26 (for customer 1st)
147.75.128.64/26 to 147.75. 128.127/26 (for customer 2nd )
147.75.128.128/26 to 147.75.128.191/26(3rd
147.75 .128.192/26 to 147.75.128.255/26(4th
147.75.129.0/26 to 147.75.129.63/26(5th)
......
147.75..159.192 /26 to 147.75.159.255/26 (last 128th customer )
so second group first address of 128 customer is 147.75.159.192/26 and
remaining address = 2^16 - (32768+8192)=16384
so B is correct