6.1 problem 147
  6.2 problem 148
  6.3 problem 149
  6.4 problem 150
  6.5 problem 151
  6.6 problem 152
  6.7 problem 153
  6.8 problem 154
  6.9 problem 155
  6.10 problem 156
  6.11 problem 157
  6.12 problem 158
  6.13 problem 159
  6.14 problem 160
  6.15 problem 161
  6.16 problem 162
  6.17 problem 163
  6.18 problem 164
  6.19 problem 165
  6.20 problem 166
  6.21 problem 167
  6.22 problem 168
  6.23 problem 169
  6.24 problem 170
  6.25 problem 171
  6.26 problem 172
  6.27 problem 173
  6.28 problem 174
  6.29 problem 175