A store has 10 identical boxed stereos to store on 3 shelves. How many ways can the boxes be stored on the shelves if: (a) there are no restrictions on the number of stereos on each shelf? (b) the top shelf must have exactly 2 stereos on it? (c) each shelf must have at least 2 stereos on it? (d) no shelf can have more than 5 stereos on it? please help me thank you