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