A double convex lens $(\mu =1.5)$ has its focal length 10 cm. What will be its focal length if it is immersed in liquid of $(\mu_1=\large\frac{4}{3})$

Question

$(a)\;\frac{10}{3}\;cm \\ (b)\;\frac{40}{3} \;cm \\ (c)\;40\;cm \\ (d)\;10\;cm$