Subnet calculation question

[Zap]

I understand subnetting is the process of borrowing host bits, but right now I've got a brain lock going on and hope someone can help break the log jam.

Using IP 200.151.140.64/27, if a class "C" prefix notation is /24, where did the additional 3 bits come from? I mean, it cannot just be an arbitrary number that someone picked out of the air. I'm sure the answer is not as difficult as it seems to me to be at the moment.

Thanks for your help.

[Biggles77]

11111111 11111111 11111111 111 00000

Does that help?

[Zap]

Thank you for your reply. I understood where the three bits came from. I was wondering how they were determined. Why 27 and not 20, for example. I did some research on the net and just happened to come across an article on IP addressing that said the network numbers in an IP address are assigned and all other numbers are up to the network administrator.

I do appreciate your response and have another IP question that I'll post on the CCNA forum. Maybe you'll have the answer.