When a system returns to its original state after completing a series of changes, then it is known that a cycle is completed. This process is known as cyclic process. In a cyclic process the initial and the final state is same. As the internal energy $U$ of the system depends only on the state of the system so in a cyclic process the net change of internal energy, $\Delta U$ will be equal to zero i.e. $\Delta U =0$. Hence from the first law $(\Delta U=Q+W)$
Hence, $W=-Q$