The refractive index of glass with respect to air is $3/2$ and refractive index of water with respect to air is $4/3$. What will be the refractive index of water with respect to glass ?

The refractive index of water with respect to glass is $8/9$.
“Refractive index is the measure of the bending of a ray of light when passing from one medium into another.”
$\mathrm{Refractive}\mathrm{index} \mathrm{of} \mathrm{a} \mathrm{medium} =\mathrm{ }\frac{\mathrm{Speed} \mathrm{of} \mathrm{light} \mathrm{in}vacuum}{\mathrm{speed} \mathrm{of} \mathrm{light} \mathrm{in} \mathrm{the}medium}$
We know that the Refractive index of glass is $3/2$ and refractive index of water is $4/3$.
So, $\mathrm{Refractive} \mathrm{index} \mathrm{of} \mathrm{water} \mathrm{with} \mathrm{respect} \mathrm{to} \mathrm{glass} =\frac{\mathrm{Refractive} \mathrm{index} \mathrm{of} water}{\mathrm{Refractive} \mathrm{index} \mathrm{of} glass}$
$\Rightarrow \mathrm{Refractive} \mathrm{index} \mathrm{of} \mathrm{water} \mathrm{with} \mathrm{respect} \mathrm{to} \mathrm{glass} =\mathrm{ }\frac{\frac{\mathrm{Speed} \mathrm{of} \mathrm{light}\mathrm{in} \mathrm{Vacuum} }{\mathrm{Speed} \mathrm{of} \mathrm{light} \mathrm{in} \mathrm{water} }}{\frac{\mathrm{Speed} \mathrm{of} \mathrm{light} \mathrm{in} \mathrm{vacuum} }{\mathrm{Speed} \mathrm{of} \mathrm{light} \mathrm{in} \mathrm{glass} }}$
$\Rightarrow \frac{4/3}{3/2} =8/9$