28.1 problem 61
28.2 problem 62
28.3 problem 63
28.4 problem 64
28.5 problem 65
28.6 problem 66
28.7 problem 67
28.8 problem 68
28.9 problem 69
28.10 problem 70
28.11 problem 71
28.12 problem 72
28.13 problem 73
28.14 problem 74
28.15 problem 75
28.16 problem 76
28.17 problem 77
28.18 problem 78
28.19 problem 79
28.20 problem 80
28.21 problem 81
28.22 problem 82
28.23 problem 83
28.24 problem 84
28.25 problem 85
28.26 problem 86
28.27 problem 87
28.28 problem 88
28.29 problem 89
28.30 problem 90
28.31 problem 91
28.32 problem 92
28.33 problem 93
28.34 problem 94
28.35 problem 95
28.36 problem 96
28.37 problem 97
28.38 problem 98
28.39 problem 99
28.40 problem 100
28.41 problem 101
28.42 problem 102
28.43 problem 103
28.44 problem 104
28.45 problem 105
28.46 problem 106
28.47 problem 107
28.48 problem 108
28.49 problem 109