14.1 problem 1
14.2 problem 2
14.3 problem 3
14.4 problem 4
14.5 problem 5
14.6 problem 6
14.7 problem 7
14.8 problem 8
14.9 problem 9
14.10 problem 10
14.11 problem 11
14.12 problem 12
14.13 problem 13
14.14 problem 14
14.15 problem 15
14.16 problem 16
14.17 problem 17
14.18 problem 18