This question looks impossibly hard at first. But work carefully and the solution is beautiful.

School Math is not enough. At Cuemath's after-school online Math classes you don't just learn Math as rules but also how to apply it with logic in real-life. Like how two 8'' medium-sized pizzas will have less Pizza compared to a 16" large pizza. Why? Because it's the surface area which needs to be counted and not the diameter. Logic Hai! | Cuemath