21,600 nautical miles, as a nautical mile is a minute of longitude at the equator, so 60 minutes in a degree times 360 degrees in a circle = 21,600 NM in 24 hours, = 900 knots ground speed is the answer they are looking for I am guessing. Either way, dragons crappy old airbuses will need a 450 knot tail wind, not very likely at the equator.