Explanation:

- The cost prices (CP) are Rs. 500 for article A and Rs. 600 for article B.

- Both articles were sold at the same selling price (SP).

- Article A's profit percentage is 2x%.

- Article B's profit percentage is x%.

To find the selling price, equate the profit amount for both:

- Profit on A: (2x/100) * 500

- Profit on B: (x/100) * 600

Since SP is the same,

$$ 500 + (2x/100) \times 500 = 600 + (x/100) \times 600 $$

Solving this gives:

$$ 500 \times (1 + 2x/100) = 600 \times (1 + x/100) $$

Solve to get SP = Rs. 750.

Hence, the correct option is:

- Option 3: Rs. 750