Hmm.. I would say it is A, assuming that Lhotse-face drove on the same track both directions..
If x is the distance travelled in each direction
Avg speed = 2x/(t1+t2)
t1 = x/4 & t2 = x/6
Avg speed = 2x / (x/4+x/6) = 4.8 SUFF
We don't know the speed of return journey.
"To dream anything that you want to dream, that is the beauty of the human mind. To do anything that you want to do, that is the strength of the human will. To trust yourself, to test your limits, that is the courage to succeed."
- Bernard Edmonds