Reading of weighing machine when solid is immersed into it using a massless string is:
Buoyant force = Weight of displaced fluid = !!rhogV = 1000xx10xx3xx10^-3 = 30N!!
Weight of block will be balanced by tension in rope.
According to newton's 3rd law, block will apply equal and opposite force on water. The reaction of buoyancy on the beaker is respoible for the increase in weight.
Hence, reading shown by weighing machine will be:
Therefore, option(b) is correct.