8.1 problem Exercise 21.3, page 231
  8.2 problem Exercise 21.4, page 231
  8.3 problem Exercise 21.5, page 231
  8.4 problem Exercise 21.6, page 231
  8.5 problem Exercise 21.7, page 231
  8.6 problem Exercise 21.8, page 231
  8.7 problem Exercise 21.9, page 231
  8.8 problem Exercise 21.10, page 231
  8.9 problem Exercise 21.11, page 231
  8.10 problem Exercise 21.13, page 231
  8.11 problem Exercise 21.14, page 231
  8.12 problem Exercise 21.15, page 231
  8.13 problem Exercise 21.16, page 231
  8.14 problem Exercise 21.17, page 231
  8.15 problem Exercise 21.19, page 231
  8.16 problem Exercise 21.20, page 231
  8.17 problem Exercise 21.21, page 231
  8.18 problem Exercise 21.22, page 231
  8.19 problem Exercise 21.24, page 231
  8.20 problem Exercise 21.27, page 231
  8.21 problem Exercise 21.28, page 231
  8.22 problem Exercise 21.29, page 231
  8.23 problem Exercise 21.31, page 231
  8.24 problem Exercise 21.32, page 231
  8.25 problem Exercise 21.33, page 231