A coil of inductance $L= 150\;mH$ and resistance $R= 70\;m \Omega$ is connected to a voltage source. How soon will the voltage attain $50\%$ of initial value

Question

$(a)\;2.82 \;s \\(b)\;1.49\;s \\ (c)\;2.49\;s \\ (d)\;0.14\;s$