Answer:
This is a very tricky and underhanded question. Leading me to believe that the person who conceived such a problem is a rascal, a knave, a person so contrary to the human that decorum prevents me from describing them further.
Well. Obviously we are tempted to answer 7 km/hr because that is the average of 6 and 8.
But the question does not suppose that she traveled for a unit of time, but a unit of distance.
Let us assume that she traveled 8km/hr for an hour in order to traverse half the distance. To travel the rest of the distance at 6 km per hour, it would take her 8/6 ths as long.
Let us agree that average speed would be distance/time.
the numerator would be (8 km + 8 km). Yes that is right because she went 8 kms at 8km/hr plus 8 kms at 6 km/ hr.
So distance over time = 16/time. But the number of hours is 2.3333.
Hence 16/2.333 = 6.86 km/hr