There are six weighing machines in the figures given above.

Water does not flow out of the container in the first set of three weighing machines. Hence, the readings shown by the weighing machine given in Figure (a) increases. The first reading is 20 N. The second reading is 25 N and the final reading is 28 N.

Water flows out of the container in the final set of three weighing machines. According to Archimedes' principle, upthrust is equal to the weight of water displaced. To support the 5N and 8N weights, water from the container flows out.

Therefore, the readings shown by the weighing machine given in Figure (b) are 30 N.