Exercises, part 2

Exercises from chapter 4-7:

4.4, 4.5, 4.11, 4.17, 4.18, 4.19, 4.34

5.1, 5.2, 5.8, 5.12, 5.16

6.4, 6.6, 6.8, 6.9, 6.10, 6.18, 6.19

7.2, 7.4, 7.5, 7.14, 7.17, 7.20, 7.21