After 6 hours forward flight they would be at: longitude 90° eastward
The Greenwich is at Longitude 0 degrees, for a flight forward in time means that the Flight direction is eastward.
The Longitude lines runs from the north pole to the south pole dividing the globe into 180° to the east and 180° to the west of the equator while crossing the equator at right angles.
Each Longitude is 15° apart from the closest longitude because the earth is divided int 24 hours ( 12 hours to the east and 12 hours to the west )
i.e. 180° / 12 hours = 15°
Therefore after 6 hours flight ( forward ) the degree of longitude they would be at = 15° * 6 = 90° eastward
Hence we can conclude that they would be at longitude 90° eastward.
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