A cubic-shaped container of side L = 12.5 cm, made of acrylic (n = 1.52) has a small stain throughout the center of the container. the entire center of the container. 3.1. What is the area of the cube that must be covered to avoid observing the stain? 3.2. After covering the area where the stain is visible, question 4.1. How much area of the cube is left uncovered? 3.3. What is the maximum index that the material of the cube can have, so that the stain can be seen from any observation point?