This sounds like a question from a book or something. Nobody uses 64k circuits. A slow cellphone internet connection will use more than 64k.
You need to reask what you really need to know. The sizing of the circuits and network is based on the traffic flow.
Frame relay is on its way out. The bandwidths requirements have grown so large that other technologies are more cost effective than messing frame relay to run fractional circuits.
Besides if you are in the US and need to meet HIPPA you need to hire some help fast. If you cannot design a simple network you will never manage to get one that works with encryption activated.
Main site have 8 departments and each department have 60 pc's,remaining sites each have 6 departments and in each department have 40 pc's and in the design of WAN connection you use frame relays and that is the 100% growng hosptals and clock speed is 64000 bits/sec and security must don't access the unautheraised users from out side....how can I do this?thanks for any help!