4. When Party B's water consumption reaches 4 tons and Party A's water consumption reaches 4*5/3 tons, the amount of water payable by Party B at this time is 4* 1.8=7.2, and that of Party A is 4 *1.8+(4 * 5/3-4) * 3 = 7.2+8/3. At this time, the water fee paid by both parties is 14.4+8/3. Since then, the water fee paid by both parties is the same price, that is, per ton of 3 yuan, so according to their water fee ratio of 5: 3, they will also pay the water fee ratio of 5: 3. And 26.4- 14.4-8/3=28/3 is the total water fee they paid afterwards. Combined with the ratio of 5: 3, it can be calculated that the water fee paid by Party B is 28/3*3/(5+3)=3.5, so the total water fee paid by Party B is 3.5+7.2.
5. Increased cost: 8-4=4 yuan, which is caused by charging the free baggage weight of two people according to the overweight, so the free salute weight of each person should be 4/2=2 yuan, that is, if it is charged according to the overweight 150kg, the cost should be 2*3+4= 10 yuan. That is, the charge per kilogram is10/150 =1/5 yuan, from which it can be inferred that the actual overweight weight of the original three people is: 4/(115) = 60 kilograms, so