The current passing through a choke coil of $5 \mathrm{H}$ is decreasing at the rate of  $2 \mathrm{A} {\mathrm{s}}^{-1}$. The emf developed across the coil is

When the current in the portion of the circuit shown in the figure is $2 A$ and increasing at the rate of $1 A s^{-1}$, the measured potential difference $V_{ab}=8V$. However when the current is $2 A$ and decreasing at the rate of $1 A s^{-1}$, the measured potential difference $V_{ab}=4V$. The values of $R$ and $L$ are