topic: 7.6
exercise: 7.6
topic: 7.7
exercise: 7.7
topic: 7.8
exercise: 7.8
topic: 7.9
exercise: 7.9
topic: 7.10
exercise: 7.10
topic: 7.11
exercise: 7.11
topic: 7.12
exercise: 7.12
topic: 7.13
exercise: 7.13
topic: 7.14
exercise: 7.14
topic: 7.15
exercise: 7.15