# Is it possible to calculate the propagation delay if only the length of the link is known & not the speed at which a bit travels into the link?

Consider a $10^7$ bps link that is $400$ km long, with a queue large enough to hold $2000$ packets.Assume that the packets arrive at the queue with an average rate of $4000$ packets per second and that the average packet length is $2000$ bits.Find the average number of packets in the queue.

I am getting Average Queue length = 0.

In this question is it possible to calculate Propagation delay?
How can we calculate the propagation delay until we don't know about the speed at which a bit travels in the link?

Yes, you can infer the propagation delay from the length of the link if you know something about the technology used to transmit the bits. As Wikipedia says, the propagation delay is equal to $d/s$ where $d$ is the distance and $s$ is the wave propagation speed. The wave propagation speed depends upon the technology and might be as fast as $c$ (the speed of light) or might be somewhat slower (e.g., for copper wire).