3.2.1 problem 15
  3.2.2 problem 16
  3.2.3 problem 17
  3.2.4 problem 19
  3.2.5 problem 20
  3.2.6 problem 22
  3.2.7 problem 23
  3.2.8 problem 24
  3.2.9 problem 26
  3.2.10 problem 27
  3.2.11 problem 30
  3.2.12 problem 31
  3.2.13 problem 32
  3.2.14 problem 33
  3.2.15 problem 34
  3.2.16 problem 36