Networking questions!

[ResidentBiscuit]

I'm currently taking a Networked Systems class. I'm studying for the transport layer chapter, and ran into a few questions giving me grief. The professor has the answers on the website for these, but they don't seem to match up right. First question:

T/F - Suppose host A sends one segment with sequence number 38 and 4 bytes of data over a TCP connection to host B. In this same segment the acknowledgement number is 42.

Online it says this is false. But if you ack the next sequence number you're expecting, wouldn't this be true?

Second question:

Host A sends data to Host B over a TCP connection. Two segments sent, first has sequence number of 65, and second has sequence number of 92. How much data is in the first segment? Suppose the first segment is lost, but the second segment arrives to Host B. What ack number will host B send to host A?

First question here I said 26 bytes. Segment one should be bytes 65 to 91, 91-65 = 26. Online it says 20 -_-
Second question here, I said ack number = 65. If Host B doesn't get the first segment but it gets the second, it would ack the missing segment sequence number. Online the professor has 90. Once again, no idea how.

Anyone think I'm right here?

[naraku9333]

The first is false because the first message sent doesnt have ack field set. AFAIK the sequence nubers are random (initially) and you cant calculate the data length that way. For the last part I think it should ack the last recieved sequence number + 1. I haven't done any of this in a while and had to check a textbook.