Step-by-step explanation:
[tex] \frac{9}{17} = \frac{3a}{a + b} \\ \\ \therefore \: 9(a + b) = 17 \times 3a \\ \\ \therefore \: 9a + 9b =51a \\ \\ \therefore \: 9b =51a - 9a\\ \\ \therefore \: 9b =42a \\ \\ \therefore \: \frac{9}{42} = \frac{a}{b} \\ \\ \therefore \: \frac{3}{14} = \frac{a}{b} \\ \\ \huge \orange{ \boxed {\therefore \: a \: \: : \: b = 3 \: : \: 14}}[/tex]
