CX/KA interviews are renowned for the odd really strange question that seems totally irrelevant and just trying to catch you out. Over the years many have tried weeding these out of the interview process but they always seem to creep back in due to the "wisenheimers" who love trying to trick people for their own personal satisfaction.
That particular gem is simply trying to ascertain whether you know where Indonesia is (roughly spread out along the equator) and what the circumference of mother Earth is at the equator. 24 hours one revolution etc.
It is a behavioral interview question dressed up as a technical question to see how a candidate uses logic to solve a problem under pressure using assumed knowledge that is applicable to the position advertised. The person is using a bit of high school maths, geography, navigation, and flight planning.
At HKGs latitude (22N) you would need to be flying M1.46 to meet the earths rotation, at the equator, M1.57, and in Jakarta (6S) M1.56 [1.57xcos(latitude)]. Track to Jakarta is 195, 4 hour flight time traveling through 28 degrees of latitude.
The other ballpark way is by looking at the earths rotation, it rotates at around 900 kts at the equator (360 degrees x 60 nm per degree/24 hours), in the 4 hours flight time to Jakarta it will rotate 3600 nm. Mach 1 is close enough to 600 kts (574 kts at FL360 on a standard day).
The answer is a big number either way, well in excess of what any airliner is capable of. It is not really relevant to passing of failing the interview. What is being assessed is the logic/problem solving, and the persons demeanor.
Think about it from a CRM problem solving model point of view. If presented with a problem one did not know the answer to on the line, would you B/S the other crew ? or would you tell they you don't really with the information you have, CLARIFY if there is additional information available (e.g. how long does it take to fly to Jakarta ?) offer your input/logic so the problem can be solved (look for solutions and evaluate) as a group.
Interviews are interactive, you can always seek additional details or clarify the problem.
Then they follow it up with two questions on what your perception of CRM is, and if you think you have good CRM. Then they have the comparison of how you put it in practice with the sunset question.
Someone has put some thought into the interview structure.