A transparent cube of side `210 mm` contains a small air bubble. Its apparent distance, when viewed from one face of the cube is `100 mm`, and when viewed through opposite face is `40 mm`. What is the actual distance of the bubble from the second face and what is the refractive index of the material of the cube ?

Explanation

To solve the problem, we will follow these steps:

### Step 1: Understand the Problem
We have a transparent cube with a side length of 210 mm containing a small air bubble. The apparent distances of the bubble from two opposite faces of the cube are given as 100 mm and 40 mm. We need to find the actual distance of the bubble from the second face and the refractive index of the material of the cube.

### Step 2: Set Up the Variables
Let:
- The actual distance of the bubble from the second face be \( X \).
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