Assume you are a tutor for university students taking accounting exams. The name of your business is Brooklyn's Tutoring Service. You charge $30 an hour. First, you pay the student newspaper $100 for advertising. After spending 3 hours helping your first student you bill him and he pays you $50 at that time and tells you he will pay the balance later. Your revenue account is named Tutor Fees. One week later he pays you $20. Prepare the journal entries to record these three transactions