While purchasing an item that costs Rs. 400, one has to pay sales tax at the rate of 7% and on another item costing Rs. 6400, the rate of sales tax was 9%. The percent of sales tax one has to pay, taking these items together on an average is?

• A. 6 13 % 16
• B. 7 14 % 17
• C. 9 18 % 15
• D. 8 15 % 17
• E. None of these