In a class, there are 43 students. Kunal's rank is $$17^{th}$$ in the class, who is ahead of Pinki by 6 ranks, Pinki being 7 ranks ahead of Balwan. If ranking system is from top to bottom, then what is Balwan's rank?

We are given that the ranking system is from top to bottom, meaning the lower values are better. 

We are given that Kunal (rank 17) is ahead of Pinki by 6 ranks, which would mean that Pinki's rank is 6 more than Kunal, $$17+6=23$$

we are then given that Pinki (rank 23) is ahead of Balwan by 7 ranks, which would mean that Blawan's rank is 7 more than Pinki, 23+7 = 30

Therefore, Option D is the correct answer.