Let a, b and c be the length of sides of a triangle ABC such that (a + b)/7=(b + c)/8=(c + a)/9 If r and R are the radius of incircle and radius of…

Let $\displaystyle \mathrm{a}, \mathrm{b}$ and c be the length of sides of a triangle ABC such that $\displaystyle \frac{\mathrm{a}+\mathrm{b}}{7}=\frac{\mathrm{b}+\mathrm{c}}{8}=\frac{\mathrm{c}+\mathrm{a}}{9}$If r and R are the radius of incircle and radius of circumcircle of the triangle ABC, respectively, then the value of $\displaystyle \frac{R}{r}$ is equal to :