[tex]0.8a = 1.6b \: = > \: a = \frac{1.6b}{0.8} = > \: a = 2b. \\ a) \: \frac{b}{a} = \frac{b}{2b} = \frac{1}{2} . \\ b) \: \frac{2a + 3b}{2a - 3b} = \frac{4b + 3b}{4a - 3b} = \frac{7b}{b} = 7. \\ c) \: \frac{a + b}{a} = \frac{2b + b}{2b} = \frac{3b}{2b} = \frac{3}{2} .[/tex]