5.1 problem 4
  5.2 problem 5
  5.3 problem 6
  5.4 problem 7
  5.5 problem 8
  5.6 problem 9
  5.7 problem 10
  5.8 problem 11
  5.9 problem 12
  5.10 problem 13
  5.11 problem 14
  5.12 problem 15
  5.13 problem 16
  5.14 problem 17
  5.15 problem 19