Answer:
It is necessary to acknowledge the SYN and FIN, so the sequence number is incremented, if not the FIN would be seen as a data packet prior an awaited FIN.
Step-by-step explanation:
TCP or transmission control protocol is a transport layer protocol of the OSI network model in networking. Unlike UDP or user datagram protocol, it is connection oriented, meaning it must establish a connection between both destination and source in the network.
It uses a three way handshake to establish and close connection after transmission. After the SYN packet is acknowledged, the sequence number of the data packet increases to the last and finally increases to a FIN packet to show the end of transmission.