Translation:Pomóżcie mi w pisaniu książki.
Why isn't option with 'Pomóż mi z napisaniem książki' accepted? :(
"napisać" is a perfective verb, so means not just writing a book but also finishing it. That being said, "Pomóż mi w pisaniu książki" should be accepted, because English you is both singular and plural, so could mean both "ty" and "wy".
w pisaniu książki. which case is it?
pisaniu is Locative (in what?), książki is Genitive (writing of what)
Am I the only one who thinks "help me with writing the book" sounds very strange?