I am learning about TCP control flow and came across a question about how much data is carried by the 4th segment. The answer is supposed to be 1200 (2230 - 1030) but I don't quite understand why.

By definition, I know that the acknowledgement number is telling the other side what is next expected from it. Thus 5 is the server acknowledging everything up to 2230 and telling the client that the server is expecting 2230 next, while 3 is the client acknowledging everything up to 3848 and telling the server that it next expects 3848. But I still don't understand why we're considering segment 5 and segment 2? If it's only "expecting" then how do we know how much data is being carried?

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The data that will be carried in the 4th segment is 1200 why?we can know it by simpley look at the sequence number of the 6th packet -a packet's sequence number is in simple words:"im sending data from this certain number" if we take a look at the 3th packet we can see that it was sent from the client to the server with a sequence number of 1030 and we can see in the 6th packet that the sequence number of it is 2230 which means a total 2230-1030=1200 of data was sent from the clinet to server in the 4th packet

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