A point object with a charge `+Q` is placed at the center of a conducting shell of inner radius `R`, outer radius 2R, and a charge of `-4Q`. A thin - walled conducting shell of radius 3 R and a charge of +4Q is concentric with the point object and the first shell. Defining V = 0 at infinity, find all the distances from the center at which the electric potential is zero .

Explanation

To solve the problem, we need to analyze the electric potential due to the charges and find the distances from the center where the potential is zero.

### Step-by-Step Solution:

1. **Understanding the System**:
- We have a point charge \( +Q \) at the center of a conducting shell with inner radius \( R \) and outer radius \( 2R \), which has a charge of \( -4Q \).
- There is another conducting shell with radius \( 3R \) and charge \( +4Q \) that is concentric with the first shell.

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