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Thirteen Oh Two

A connection opens with the client's ISN at 100 and the server's at 300, exactly as in RFC 9293's Figure 6. Then:

# direction segment
1 C to S SEQ=100, CTL=SYN
2 S to C SEQ=300, ACK=101, CTL=SYN,ACK
3 C to S SEQ=101, ACK=301, CTL=ACK
4 C to S SEQ=101, 1200 bytes of data
5 S to C ACK=?
6 C to S SEQ=?, CTL=FIN
7 S to C ACK=?

What is the acknowledgment number in segment 7?