10
cubic metre
The maximum water fee is 1.6* 10= 16.
11-15m3
Pay the water fee at most.
16+5*2=26
It cost 33.5 yuan
The cost above 15 is 33.5-26=7.5. The cost above 15 is 2.5 cubic meters, so the total cost is 17.5 cubic meters.