David took a lease of a shop from Ken for a fermof ve years. David set up a business of importing rugs from an overseas supplier and selling them from his leased shop premises. initially, business was good and David was able to trade profitably. However, after two years had passed, David's business declined seriously for two reasons. First, a shopping centre opened up nearby and an opposition rug retailer with substantial capital resources started to undercut David's prices. This resulted in a \"price war" developing, and David had to reduce his prot margin considerably to retain some market share. Secondly, David's offshore souroe of supply of product ceased for reasons beyond David's control and the landed cost of his product increased dramatically. David approached Ken and informed him that he could no longer afford the agreed rental on the shop and would have to leave. Ken promised to reduce the rent if David remained in the shop as his tenant. The reduced rental was paid by David for the remaining three years of the lease. When the lease expired, Ken claimed from David the rental at the full rate for the last three years. Advise David whether he is legally liable to pay the rent that Ken had agreed to waive (write-off), using cases to support your conclusion. {5 marks}