A A client server system uses a satellite network with the satellite at a height of 40000 km What is the best-case delay in response to a request?

The best-case delay is the time it takes for a signal to travel the round trip of 80,000 km to the satellite and back. Since electromagnetic signals travel at the speed of light, we have the following:

80,000,000 m / 299,792,458 m/s .= 0.267 seconds