How to calculate the sewage treatment fee of Shanghai residents

2 yuan is the water fee, plus 10% as the sewage treatment fee, so the sewage treatment fee is 2*0.9= 1.8 yuan, that is, the total water fee is 20*3.8=76 yuan. If the water fee is paid to 57 yuan, the water consumption is 57/3.8= 15 tons.