Aplane is 300 miles west of city a, and is flying west at 600 miles per hour. how long will it take for the plane to be 2490 miles west of city a?

The aircraft is already 300 miles west of A,
so it only has (2490 - 300) = 2190 more miles to go.

                        (2190 miles) / (600 miles/hour)

                   =  (2190 / 600) hours

                   =      3.65 hours

                   =        3 hours  39 minutes  more.