Step 1: Understanding the problem.
Let the cost price of each article be \( C \). The total cost price of 76 articles is \( 76C \). The total profit is given as Rs 6570. We need to find the value of \( C \).
Step 2: Calculating the profit from each group of articles.
- Profit from 20 articles sold at 15% profit: \( 20 \times C \times 0.15 \)
- Profit from 40 articles sold at 19% profit: \( 40 \times C \times 0.19 \)
- Profit from 16 articles sold at 25% profit: \( 16 \times C \times 0.25 \)
Now, the total profit is the sum of the profits from all three groups, which is given as Rs 6570. After solving, we find that \( C = 420 \).
Step 3: Conclusion.
The correct answer is (C) Rs 420, as this is the cost price of each article.