A trader maintains his books of accounts on Single Entry basis. His books of accounts show that his total purchases during the year were Rs. 90,000 of which he returned goods worth Rs. 10,000. His credit sales were Rs. 50,000 and cash sales were Rs. 80,000 of the total sales goods returned were Rs. 30,000. Closing stock is Rs. 12,000. He sells his goods at cost plus $$33\frac{1}{3}\% .$$  His opening stock is: