The densities of two solid spheres A and B of the same radii R vary with radial distance r  as  ${\rho }_{A\left(r\right)}=k\left(\frac{r}{R}\right)$  and  ${\rho }_{B\left(r\right)}=k{\left(\frac{r}{R}\right)}^5,$  respectively, where k is a constant. The moment  of inertia of the individual spheres about axes passing through their centres are  $I_A$  and  $I_B$  respectively. If  $\frac{I_B}{I_A}=\frac{n}{10},$ the value of n is