Subnetting is always fun, it's what my students get hung up on the most...

For Class A networks the default subnet mask is this: 255.0.0.0

Represented as Network (N) bits and Host (H) bits:

NNNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH

For Class B networks the default subnet mask is this: 255.255.0.0

Represented as Network (N) bits and Host (H) bits:

NNNNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH

For Class C networks the default subnet mask is this: 255.255.255.0

Represented as Network (N) bits and Host (H) bits:

NNNNNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH

The equation for the amount of networks you can have in your new subnet after borrowing Host bits to make more Network bits is this: 2 ^ (# of borrowed H bits)

The equation for the amount of hosts you can have in your new subnet after borrowing is this: [2 ^ (# of remaining H bits)] - 2

(The "-2" at the end is to account for the Network ID and Broadcast ID addresses)

The equations remain the same regardless of what IP class you're dealing with. As the number of network (N) bits increase, the number of host (H) bits decrease - more networks, but less hosts in each network. As the number of network (N) bits decrease, the number of host (H) bits increases - less networks, huge blocks of hosts.

I hope this helped - if not lemme know and I'll explain it another way.