Judy's Pies sells an average of $12,100 of pies each month without advertising. In July, while running an online ad campaign that cost $ 500, the store sells $14,635 worth of pies. No other promotions were offered during July, but a 10% discount was offered in August. What is Judy's Pies ad campaign lift %?

A. 32%

B. 18%

C. 21%

D. 25%