Rubin Enterprises had the following sales-related transactions on a recent day: a. Billed customer $28,900 on account for services already provided. b. Collected $5,955 in cash for services to be provided in the future. c. The customer complained about aspects of the services provided in Transaction a. To maintain a good relationship with this customer, Rubin granted an allowance of $1,600 off the list price. The customer had not yet paid for the services. d. Rubin provided the services for the customer in Transaction b. Additionally, Rubin granted an allowance of $320 because the services were provided after the promised date. Because the customer had already paid, Rubin paid the $320 allowance in cash. Required: Prepare the necessary journal entry (or entries) for each of these transactions.