X+Y+Z=3.3
①
X/3
+
Y/4
+
Z/5
=
5 1/60
②
Z/3
+
Y/4
+
X/5
=
53.4/60
③
20x+15y+12z = 51is obtained from Equation 2.
④
20Z+ 15Y+ 12X=53.4 is obtained from formula ③.
⑤
Z-X=0.3 from ⑤-④, then Z=X+0.3.
⑥
If Formula 6 is brought into Formula 1, X+Y+X+0.3=3.3, then Y=3-2X.
⑦
Bring the formula ⑥ ⑥ into the formula ⑥ and get 20x+15 (3-2x)+12 (x+0.3) = 51,so X= 1.2.
Y=0.6，Z= 1.5
So from A to B, it is 1.2km uphill, 0.6km flat slope and 1.5km downhill.