Sam is the owner of a scallop boat. In 2015, Sam leased the vessel to his friend, Stevenson, for 10 years as an annual rental of $10,000. In 2017, it became apparent that scallop numbers were declining and Stevenson soon realised that he would be unable to meet the annual rental charge unless the catch is improved. He approached Sam and advised him of his fishing and financial difficulties. He also complained that the engine in the scallop boat was not as powerful as he had been led to believe. Sam denied that he had ever made any promises or statements about the engine power. However, he said that he was prepared to halve the annual rental until the catch improved and, accordingly, the rental charge was reduced to $5,000. In 2020, the catch improved to such an extent that Stevenson is able to resume paying $10,000 a year. Sam was delighted and advised Stevenson that not only did he have to pay $10,000 a year until 2025, but also the $15,000 forgone by Sam in the previous three years.

Advise Stevenson whether he must pay the $15,000 claimed by Andrew.

Answer should be done using the IRAC (Issue, Rule, Analysis and Conclusion) method and referred using the Australian Contract Law. I need help on how to structure the answer in detail. Please also refer the exact excerpt from the law.