From above picture, we can see the length of UDP is 58 bytes, the length of the UDP payload is 50 bytes, so the length of each of the UDP header fields is 58 - 50 = 8 bytes. You can verify the packet whose length is 93 bytes.
The length indicates the number of bytes in the UDP segment(header plus data).
50 bytes.
From above picture, we can see source port number is 4334, the hexadecimal is 10ee. So when the hexadecimal is ffff, the largest source possible port number is 65535.