Question: At the beginning of this chapter you surveyed the 87 computer users who subscribe to your electronic newsletter in preparation for the release of your new software product. The results of your survey reveal that of the 87 subscribers, 68 have a Windows-based system available to them, 34 have a Linux system available, and 30 have access to a Mac. In addition, 19 have access to both Windows and Linux systems, 11 have access to both Linux systems and Macs, and 23 can use both Macs and Windows. Use the principle of inclusion and exclusion to determine how many subscribers have access to all three types of systems.