Translation:How long is the Yangtze?
You don't get the pun here, do you?
(It's that "Yangtze" has 长 in it, which means long. This question asks how "长" “Long River” (长江 ) is. The "River" part is already included in the name "Yangtze", which I'm guessing is a dialectical reading of the characters 长江.
Of course you wouldn't think of this when speaking English, but we are l learning Chinese here, so I think it. would be good to keep that nuance in mind.
In Chinese 江 is supposed to be a large river whereas 河 is a river or a watercourse, but 长江 is so famous that it is also known simply as 江.
长江 is 6300 km long and is the world's third largest river, while 黄河 (mentioned elsewhere in this section) is 5464 km long and is one of the most important birthplaces of ancient Chinese civilization.