An organization has a class B network and wishes to form subnets for 64…

Key idea: determine how many bits to borrow from the host portion of a Class B network to create 64 subnets.

• Step 1: Start with Class B default mask = /16 (255.255.0.0).

• Step 2: Find smallest n such that 2^n ≥ 64. n = 6 because 2^6 = 64.

• Step 3: New prefix length = 16 + 6 = /22. Convert /22 to dotted decimal: 255.255.252.0.

• Step 4: Hosts per subnet = 2^(16 - 6) - 2 = 2^10 - 2 = 1022 usable hosts.

• Note on other choices: 255.255.0.0 is the default /16 (no subnets). 255.255.128.0 is /17 (only 2 subnets). 255.255.64.0 is not a valid contiguous subnet mask.

Final answer: 255.255.252.0 (/22).