Answer:
Class A network 100.0.0.0/8, we need to divide it so that it can use 11 department, therefore 2^{4} = 16 maximum subnet. The subnet mask 255.240.0.0/12. The hosts per subnet are 2^20 = 1048574. The first 5 subnet range is attached with this question.
Explanation:
The IP address is 32 bits, The default subnet of class A is 255.0.0.0/8, but in this case we take 4 bits from host and add it to network bits so 8+4 = 12, that's why mask bit is 12.
8 bits + 8 bits + 8 bits + 8 bits
100 . 0 . 0 . 0
we take 4 bits from 2nd octet so that it can use in 11 departments, so the remaining 4 bits + 8 bits + 8 bits = 20 bits
2^{20} = 1048574 hosts in each subnet
2^ {4} = 16 subnet ( 0 to 15 range)
when we subtract 255-15 = 240 so that the subnet mask is 255.240.0.0 / 12
