Raymond is the owner of a scallop boat. In 2015, Raymond 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 Raymond 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. Raymond 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. Raymond 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 Raymond in the previous three years. Advise Stevenson whether he must pay the $15,000 claimed by Raymond.

The answer should be using IRAC (Issue, rule, application and conclusion) method and referred to the Australian Consumer Law. I need help on how to structure it and any key references that I should mention to answer it in detail. Also, if you can list the exact law excerpts that are used as a point of reference. Many thanks, your answers are kindly appreciated.