Athin spherical glass shell in air is filled with an unknown liquid. a horizontal parallel light beam is incident on the shell and it is observed that the light is brought to focus on the surface of the shell directly opposite of the incoming beam. what is the refractive index of the liquid?
ie. the answer is 2- i just don't know how they got there

Determine the change in width a, height b, thickness t when a plate is subjected to the uniform distributed load and is made of material having modulus of elasticity e=230 gpa and poisson's ratio ν=1/3. given : a=400 mm and b= 300 mm also the uniformly distributed load in downward y direction of plate is 2 mn/m and in the positive x direction is 3 mn/m and t=20 mm