Identify typical source documents that authorize or justify a transaction to be recorded via journal entry on the general ledger for the below four transaction types (e.g. a sales invoice or bill of lading justifies recording a sale on the books):

a. Recording a fixed asset (equipment) on the books after a recent purchase

b. Increasing your allowance for bad debts at year-end.

c. Debiting retained earnings and crediting dividends payable on the books at month-end.

d. Recording a bank service charge for the month on the books.

e. Wages earned by workers in a factory.