The correct answer is aquella, because we would use the word if there was a difference in the distance. Like if you were in the right corner of a room, and the guitar was at the left corner of the room. And another reason is because aquella is feminine and in spanish, guitar is feminine.
I don't speak much Spanish but Mucho todos preferimos la pared con imigos
Answer: Cuestan.
Explanation: Cuanto means How much in english, so the question is asking how much those books are going to cost. Whenever you see a Cuanto in a question like that, assume it's talking about a number of something, or money. So Cuestan means cost, in the terms of "How much does this item cost?".