Could use some help solving this problem:

A company has 20 computers total. Out of these 20 computers, 9 run web servers and 12 host databases. In addition, 8 machines offer file sharing. Note: a particular machine can offer multiple service. In fact, 2 computers proved web services, databases, and file sharing concurrently. Given this information a) If a computer is selected at random, what is the probability that it hosts a database? b) Out of the 12 machines that host databases, one fourth of them offer file sharing. How many of the database machines don't provide sharing? c) Suppose a web server is selected at random. The probability that this computer provides file sharing is 1/3. If a file sharing machine is chosen randomly, what is the probability that it is also a web server? d) Out of the computers that run databases, 5 also offer web services. If a database server is selected at random, what is the probability that it does not offer any other services?