3. (7 points) There are 9 blue, 7 red, and 14 white light bulbs. In how many ways can they be arranged into a garland (using all the bulbs) so that no two white bulbs are adjacent?
Answer: 7779200

Solution: First, arrange all the blue and red bulbs in $C_{16}^{9}$ ways. In the gaps between them and at the ends, choose 14 positions and insert the white bulbs. There are $C_{17}^{14}$ ways to do this. In total, there are $C_{16}^{9} \cdot C_{17}^{14}$ ways to compose the garland from the available bulbs.