(b) $P = \frac{V^{2}}{R} \Rightarrow \frac{P_{1}}{P_{2}} = \frac{R_{2}}{R_{1}} \Rightarrow \frac{6}{P_{2}} = \frac{4}{6} = \frac{2}{3} \Rightarrow P_{2} = 9\ W$
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.