21. During 2019, Purple Inc. had sales on account of $198,000, cash sales of $81,000, and collections on account of $126,000. In addition, they collected $2,175 which had been written off as uncollectible in 2017. As a result of these transactions, the change in the accounts receivable balance indicates a a. $69,825 increase. b. $72,000 increase. c. $150,825 increase. d. $153,000 increase