Excellence, Inc., places a coupon in each box of its product. Customers may send in ten coupons and $2.50, and the company will send them a CD. Sufficient CDs were purchased at $6 a piece to meet the expected demand. A certain number of boxes of product were sold in 2020 . It was estimated that a total of 6% of the coupons will be redeemed. In 2020, 18,000 coupons were redeemed. Mailing costs were $0.75 per CD. At December 31, 2020, the following adjusting entry was made to record the estimated liability for premium outstanding: Required: Compute the number of boxes of product sold by Excellence in 2020