A reconnaissance plane flies 589 km away from
Its base at 764 m/s, then flies back to its base
At 1146 m/s.
What is its average speed?
Answer in units of m/s

Speed is a scalar. So, it depends on distance.

Average speed = Distance traveled / time taken

For its journey away from its base, the time taken by the plane = 589000 / 764 =770.94 s
For its journey back to base, time taken = 589000 / 1146 = 513.96 s
Total time of ride = 770.94 + 513.96 = 1284.90 s

Total distance traveled = 589 km + 589 km = 1178 km = 1178000 m

Therefore, average speed = 1178000 / 1284.90 = 916.80 m/s