Advanced Higher Chemistry question - equilibrium (anyone can help!)

Hi
I am stuck on this question (I know b and have an answer for c (I got 6.63 but I have no idea if this is right)
I am not sure what part a is asking of me? It just sounds like it wants me to write formula Kw=[H+][OH-] but that surely can't be right? I will try attach the photo as a response to this Thank you!

Look at the marking, it's 1 mark, all they want is the correct expression

Hi
I am stuck on this question (I know b and have an answer for c (I got 6.63 but I have no idea if this is right)
I am not sure what part a is asking of me? It just sounds like it wants me to write formula Kw=[H+][OH-] but that surely can't be right? I will try attach the photo as a response to this Thank you!

You have deduced a) correctly.

You have the correct answer for c). The key is realising that for pure water [H+] = [OH-] and therefore Kw = [H+]^2 (For pure water only)
I think you must have realised this judging by your correct answer.