Can you show me from zero, how do you get the answer for this question?

Host A and B are communicating over a TCP connection, and Host B has already received from A all bytes up through byte 126. Suppose Host A then sends two segments to Host B back- to- back. The first and second segments contain 80 and 40 bytes of data, respectively. In the first segment, the sequence number is 127, the source port number is 302, and the destination port number is 80. Host B sends an acknowledgment whenever it receives a segment from Host A. (a) In the second segment sent from Host A to B, what are the sequence number, source port number, and destination port number? (b) If the first segment arrives before the second segment, in the acknowledgment of the first arriving segment, what is the acknowledgment number, the source port number, and the destination port number? (c) If the second segment arrives before the first segment, in the acknowledgment of the first arriving segment, what is the acknowledgment number? (Hint: The reliability control used in TCP is basically a GBN approach with some variation.) (d) Suppose the two segments sent by A arrive in order at B. The first acknowledgment is lost and the second acknowledgment arrives after the first time-out interval. Draw a timing diagram, showing these segments and all other segments and acknowledgments sent. (Assume there is no additional packet loss.) For each segment in your figure, provide the sequence number and the number of bytes of data; for each acknowledgment that you add, provide the acknowledgment number. (hint: draw all the segments and ACKs that are exchanged between Hosts A and B involved in delivering these two segments)