The quantities $P, Q$ and $R$ are functions of time and are related by the equation $R=P Q$. Assume that $P$ is increasing instantaneously at the rate of $8 \%$ per year and that $Q$ is decreasing instantaneously at the rate of $2 \%$ per year. That is, $\frac{P^{\prime}}{P}=0.08$ and $\frac{Q^{\prime}}{Q}=-0.02$. Determine the percentage rate of change for $R$.