1.5×40/60+3×30/60 = 1+ 1.5 = 2.5km。
Charter time: 1 1-9=2 hours.
2 hours includes several 40 minutes:
60×2÷40=3
Xiaoming's boat can be farthest from the place where he rents a boat;
2.5×3 = 7.5 km.