A shopkeeper bought article ‘A’ for Rs. ‘x’ and marked it 25% above its cost price and sold it for Rs. 4000. Marked price of article ‘B’ is Rs. 800 more than that of article ‘A’ while selling price of article ‘B’ is Rs. 200 more than that of ‘A’. Find the cost price of article ‘A’ if article ‘B’ is sold at a discount of 20%.