12.1 problem 1
12.2 problem 2
12.3 problem 3
12.4 problem 4
12.5 problem 5
12.6 problem 6
12.7 problem 7
12.8 problem 8
12.9 problem 9(a)
12.10 problem 10
12.11 problem 11
12.12 problem 12
12.13 problem 13
12.14 problem 16
12.15 problem 17
12.16 problem 18
12.17 problem 19
12.18 problem 20
12.19 problem 21
12.20 problem 22
12.21 problem 23
12.22 problem 24
12.23 problem 25
12.24 problem 26
12.25 problem 27
12.26 problem 31
12.27 problem 33
12.28 problem 34
12.29 problem 35
12.30 problem 36
12.31 problem 37
12.32 problem 39
12.33 problem 40
12.34 problem 41
12.35 problem 42
12.36 problem 43
12.37 problem 44