3,72-54 =18,54/18 = 3, that is, when Dad takes the third step, it coincides with when Xiaoming takes the fourth step. At this time, the father and son left 3+3=6 footprints, and then it was the same cycle. 60/6= 10, that is, there are six such cycles. Calculate the length of each cycle: 72*3+54*4, multiplied by 6, is the perimeter of the garden. Divide the perimeter by 3. 14, it is the diameter, half of the diameter is the radius, and the square of the radius multiplied by 3. 14 is the area.

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