5 bits are necessary to create up to 30 subnets.
192 is equal to 2 bits borrowed 2^2 = 4 the number of subnets and host are 64 because 2 bits borrowed from the 8 bits of a class C network is 6, therfore 2^6 = 64.
When you borrow bits for a subnet you are intruding into the client portion of an IP address. As a result, you will lose clients in your network because the "borrowed" portion becomes the extended network prefix. This allows you to separate your bigger network into smaller, logical networks (subnets). The number of bits borrowed will indicate the total number of smaller subnets that you can support in your network. In each case, regardless of class of address, borrowing 4 bits gives a total of 14 subnets (in the classical sense) and 16 subnets (in Cisco).
Depending on class of network you are planning to use. For class C you can create much more then that (and for the most case for others too).
255.255.0.0
20
- is A
network class network address number of subnets required number of host per subnet
Yes - this is a broadcast address for all subnets in the 11.0.0.0 network.
255.255.255.0
14
The IP address 172.30.0.0 is a private IP address in the Class B range, which has a default subnet mask of 255.255.0.0 (or /16). If you use the default mask, you can create 65,536 addresses (2^16), allowing for 65,534 usable hosts per subnet (subtracting 2 for the network and broadcast addresses). If you further subnet this address, the number of subnets and hosts per subnet will depend on the subnet mask you choose. For example, using a /24 subnet mask would give you 256 subnets with 254 usable hosts in each.
A classful class B network has a network range of 128 - 191. For host addresses, anything that is legal for an IP address in the last 2 octets would be a valid host address for a class B with no subnets.