12.1 problem 19.1 (a)
12.2 problem 19.1 (b)
12.3 problem 19.1 (c)
12.4 problem 19.1 (d)
12.5 problem 19.1 (e)
12.6 problem 19.1 (f)
12.7 problem 19.2 (a)
12.8 problem 19.2 (b)
12.9 problem 19.2 (c)
12.10 problem 19.2 (d)
12.11 problem 19.2 (e)
12.12 problem 19.2 (f)
12.13 problem 19.3 (a)
12.14 problem 19.3 (b)
12.15 problem 19.3 (c)
12.16 problem 19.3 (d)
12.17 problem 19.4 (a)
12.18 problem 19.4 (b)
12.19 problem 19.4 (c)
12.20 problem 19.4 (d)
12.21 problem 19.4 (e)
12.22 problem 19.4 (f)
12.23 problem 19.4 (g)
12.24 problem 19.4 (h)
12.25 problem 19.4 (i)
12.26 problem 19.4 (j)