The difference of speed of light in the two media $A$ and $B\left(v_A-v_B\right)$ is $2.6 \times 10^7 \mathrm{~m} / \mathrm{s}$. If the refractive index of medium $B$ is 1.47 , then the ratio of refractive index of medium $B$ to medium $A$ is : (Given : speed of light in vacuum $\left.c=3 \times 10^8 \mathrm{~ms}^{-1}\right)$