(b) Maximum density of water is at $4℃$ $Also\ \frac{C}{5} = \frac{F - 32}{9} \Rightarrow \frac{4}{5} = \frac{F - 32}{9} \Rightarrow F = {39.2}^{o}F$
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.