Rupert works as an accountant in an accounting firm called Universal Accounting Solutions owned by Tim Tom and situated in Sydney. Tim is working long hours to meet an audit deadline of a big corporate client named Green Protect Ltd (Green) and asks Rupert to work on Sunday, his only day off. Rupert agrees and works 7 days a week for 2 weeks to assist Tim. Tim is able to deliver the audited financial report to Green with the help of Rupert within the stipulated time, for which Tim receives $5,000 in addition to the contracted fees. Tim is delighted to have received the extra money and promises Rupert a bonus of $1,500 for his hard work. Later that week, they have an altercation over an issue unrelated to the audit of Green's account. Consequently, Tim is disappointed and tells Rupert that he can forget about the bonus. Rupert seeks your advice on whether he can sue Tim for the $1,500 bonus.

Your Task: Explain the three essential elements of a valid contract in connection with the facts provided and advise Rupert whether he has a good chance of winning against Tim in a suit for breach of contract. You must refer to the relevant case law and legislation where necessary to support your advice.