The average sales of a mobile shopkeeper was 15 mobiles per week, to increase the sales he decided to tie up with a finance company for providing mobiles to customers on installment. After the launch of this scheme his average sales increased to 21 mobile per week. The annual percentage increase in the sales of mobile was:

• A. 40%
• B. 140%
• C. 42 6 % 7
• D. 39.33%
• E. None of these