You have the Class B network 172.16.0.0/16 and want to create 16 subnets. What will the new subnet mask be for the 16 subnets?

A /18 mask would provide 2^(18-16) = 2^2 = 4 subnets, which is insufficient.

A /19 mask would provide 2^(19-16) = 2^3 = 8 subnets, which is insufficient.

A /21 mask would provide 2^(21-16) = 2^5 = 32 subnets, which is more than needed.

A /17 mask would provide 2^(17-16) = 2^1 = 2 subnets, which is insufficient.

A /22 mask would provide 2^(22-16) = 2^6 = 64 subnets, which is more than needed.

Starting with a /16 network, to create 16 subnets, you need 2^n >= 16. This requires borrowing 4 bits (since 2^4 = 16). Adding these 4 borrowed bits to the original /16 prefix length results in a new subnet mask of /20.