i got this question wrong can you explain me why its for network security

2- Answer the following: u Consid er the following figure of a network with nodes A, B, C, D and E. Arrows represent the communication in a bidirectional secure wa a. How many keys do we have to generate such that the nodes can communicate over the arrows in a bidirectional secure way using a symmetric encryption algorithm? b. We replace the symmetric encryption algorithm with a public key system. How many public keys do we have to generate in this case