You will need the Silver Arrows to kill Ganon. Link can use them only if he has both the Bow and an Arrow. For each Arrow Link shoots, he looses one Ruby. Oh, by the way, there are some enemies that can be disposed of using only the Bow and Arrow. So be alert!
Find the Silver Arrows: From the beginning of Level Nine, go up two screens, left one, through the Secret Passage, then right two, up one, left one (bomb the wall), through another Secret Passage, left two, through yet another Secret passage, then up one (bomb the wall), and through the last Secret Passage.