Distance is constant, speed is inversely proportional to time. In this problem, the ratio of the speed up the mountain to the speed down the mountain is 60: 80 = 3: 4.

The time to go up the mountain should be inversely proportional to the time to go down the mountain, which is 4: 3.

The climbing time is 70 × 4/(4+3)=40 (minutes).

Distance: 60 × 40=2400 meters

Round trip * * * line: 2400 × 2=4800 (meters)