Answer :
64000 clock rate is used for serial interfaces to ensure effective and timely communication between two routers.
These two routers are connected to communicate using a serial cable connection, one end of the router will be using DTE (Data Terminal Equipment) and the other end uses DCE (Data Communication Equipment).
These two routers are connected to communicate using a serial cable connection, one end of the router will be using DTE (Data Terminal Equipment) and the other end uses DCE (Data Communication Equipment).