If a/b = 7/9, b/c = 3/5 , then the value of a : b : c is?

Answer: Option A

$$\begin{array}{rl}& \frac{a}{b}=\frac{7}{9},\frac{b}{c}=\frac{3}{5}\\ & \therefore a:b:c\\ & 7:9\\ & 3_{\times 3}:5_{\times 3}\\ & \overline{7:9:15}\end{array}$$