3.1.1 problem 1
3.1.2 problem 2
3.1.3 problem 3
3.1.4 problem 4
3.1.5 problem 5
3.1.6 problem 7
3.1.7 problem 8
3.1.8 problem 9
3.1.9 problem 10
3.1.10 problem 12
3.1.11 problem 13
3.1.12 problem 14