Solution: Assuming that the water consumption in March is X cubic meters, then the water consumption in April is (20-x) cubic meters.

1) If x≤6, then 20-x > 10.

At this time, 6x+6 * 6+4 * 4+8 (20-x-10) = 64,

The solution is x=34, which doesn't matter.

2) if 6 < x ≤ 10, then (20-x) > 10,

At this time, 6 * 6+4 (x-6)+6 * 6+4 * 4+8 (20-x-10) = 64.

The solution is x=20, which is irrelevant.

So there is something wrong with your topic. 4 yuan per cubic meter that may exceed 6 cubic meters and not exceed 10 cubic meter.

Four dollars is wrong.