1.1 problem 6
1.2 problem 7
1.3 problem 8
1.4 problem 9
1.5 problem 10
1.6 problem 11
1.7 problem 12
1.8 problem 13
1.9 problem 14
1.10 problem 16
1.11 problem 17
1.12 problem 18
1.13 problem 19