Explanation:

Certainly! Let's break down the problem to find the correct option.

- Cost Ratio: The cost prices of articles A and B are in the ratio 4:5. Let the cost price for A be 4x and for B be 5x.

- Selling Prices: Article A has a 10% profit. So, its selling price is \(1.1 \times 4x = 4.4x\). Article B has a 20% profit, making its selling price \(1.2 \times 5x = 6x\).

- Price Difference: The difference in selling price is given by \(6x - 4.4x = R480\). This simplifies to \(1.6x = 480\), giving \(x = 300\).

Now, to find 300% of the total cost price:

- Total Cost Price: The combined cost price is \(4x + 5x = 9x = 9 \times 300 = 2700\).

- 300% Calculation: \(3 \times 2700 = 8100\).

- Answer: The correct answer here is 810.

$$ \textbf{Option 4: } 810$$