Some hardly hikers start on a walk at 2:00 PM and return at 8:00 PM. Their speed is 4 miles per hour on level land, 3 miles per hour uphill, and 6 miles per hour downhill. How many miles was their hike?
You need to assume that the uphill distance is the same as the downhill distance.
romsek is right - you need to show some of your own work. But I'll get you started. Start by letting x be the uphill (and downhill) distance and d be the total distance.