Solution: If the climbing time is x hours and the downhill time is (2-X) hours, the uphill time is y hours and the downhill time is (2.5-y) hours when you come back.

Therefore, the equation set 3X+4.5y= 1 1.25 can be established.

4.5X+3y=9

After finishing, we can get: 4.5x+6.75y= 16.875 ①.

4.5x+3y=9 ②

①-② Score: 3 3..75y=7.875.

y=2. 1

Substitute y=2. 1 into ② to get x=0.6.

∴x=0.6h 2-x = 1.4h y = 2. 1h 4.5-y = 2.4h

∴ Total distance = 3× 0.6+4.5×1.4 = 8.1km.