Question 252110
E. 22km
For a round trip, she must walk equal amounts of time uphill and downhill, so the non-level ground part of her trip she averages 4 km/hr (average of 2 km/hr and 6 km/hr).  The level ground part of her trip she averages 3 km/hr.  Therefore, for a 6 hour trip, the distance must be greater than (but not equal to) 18 km and less than (but not equal to) 24 km.  The only choice that fits is E. 22 km.