As shown in the figure, a paddle wheel is linked to a mass of 12 kg...

The container is given to be adiabatic. By definition, an adiabatic process is one in which there is no heat transfer between the system and its surroundings.

Therefore, the heat given to the liquid is $Q = 0 \text{ J}$.

The descending mass does mechanical work on the liquid ($W = mgh = 12 \times 10 \times 0.7 = 84 \text{ J}$), which increases its internal energy, but the heat transferred remains zero.