Aray of light is traveling in a glass cube that is totally immersed in water. you find that if the ray is incident on the glass– water interface at an angle to the normal larger than 48.7°, no light is refracted into the water. what is the refractive index of the glass?

According to an observer on earth, planet x is stationary. maria and samir depart earth on their spaceships at the same time, each flying at 0.5c. maria flies toward planet x and samir flies in the opposite direction. according to maria, her voyage to planet x takes 9 years. how many years does maria's voyage take according to samir?