255.224.0.0

gives no of 1's followed by no. of 0's

where 1 represent network portion

here no. of 1's = 11

so, NID +SID = 11

SID =11-NID

=11-8(class A)

=3 bits are used for subnets

no. of sub network= 2^3-2 =6

but 6 is not in the option so in that case we consider, no. of subnets as 2^3 which is 8

answer is (B)

gives no of 1's followed by no. of 0's

where 1 represent network portion

here no. of 1's = 11

so, NID +SID = 11

SID =11-NID

=11-8(class A)

=3 bits are used for subnets

no. of sub network= 2^3-2 =6

but 6 is not in the option so in that case we consider, no. of subnets as 2^3 which is 8

answer is (B)