Question

$$\begin{matrix} & P = \overline{A} \\ & Q = \overline{B} \\ & R = \overline{\overline{A} + \overline{B}} = \overline{\overline{AB}} = AB \\ & \text{ }S = \overline{AB}\ \Rightarrow \text{~}\text{NAND Gate}\text{~} \end{matrix}$$