A shopkeeper buys 700 pens which cost him Rs. 500 per 100 pens. He also buys 500 pencils which cost him Rs. 700 per 100 pencils. He then sells off all the pens and pencils at Rs. 7 per piece. What percentage of profit on his cost does he make overall?

• A. 20 percent
• B. 10 percent
• C. 30 percent
• D. 40 percent