3.1 problem 55
  3.2 problem 56
  3.3 problem 57
  3.4 problem 58
  3.5 problem 59
  3.6 problem 60
  3.7 problem 61
  3.8 problem 62
  3.9 problem 63
  3.10 problem 64
  3.11 problem 65
  3.12 problem 66
  3.13 problem 67
  3.14 problem 68
  3.15 problem 69
  3.16 problem 70
  3.17 problem 71
  3.18 problem 72
  3.19 problem 73
  3.20 problem 74
  3.21 problem 75
  3.22 problem 76
  3.23 problem 77
  3.24 problem 78
  3.25 problem 79
  3.26 problem 80
  3.27 problem 81
  3.28 problem 82
  3.29 problem 83