If a business books a cleaner on 15 April, their office is cleaned on 15 May, the cleaner gives them an invoice on 30 May, and the business pays the invoice in cash on 30 June, when was the office cleaning expense incurred under accrual accounting principles? Select one: 1. 15 April 2. 15 May 3. 30 May 4. 30 June 5. none of the above