Exercise $6-6($Static$)$ Performance obligations; customer option for additional goods or services; residual method $[$LO$6-2,6-4,6-5,6-6]$

Clarks Incorporated, a shoe retailer, sells boots in different styles. In early November, the company starts selling $$SunBoots$$ to customers for $$70$ per pair. When a customer purchases a pair of SunBoots, Clarks also gives the customer a $30\%$ discount coupon for any additional future purchases made in the next $30$ days. Customers can$$t obtain the discount coupon otherwise. Clarks anticipates that approximately $20\%$ of customers will utilize the coupon, and that on average those customers will purchase additional goods that normally sell for $$100.$