7.1 problem 1
  7.2 problem 2
  7.3 problem 3
  7.4 problem 4
  7.5 problem 5
  7.6 problem 6
  7.7 problem 7
  7.8 problem 8
  7.9 problem 9
  7.10 problem 10
  7.11 problem 11
  7.12 problem 12
  7.13 problem 13
  7.14 problem 14
  7.15 problem 15
  7.16 problem 16
  7.17 problem 33
  7.18 problem 34
  7.19 problem 35
  7.20 problem 36
  7.21 problem 37
  7.22 problem 38
  7.23 problem 39
  7.24 problem 40
  7.25 problem 41
  7.26 problem 42
  7.27 problem 52
  7.28 problem 53
  7.29 problem 54
  7.30 problem 55
  7.31 problem 56