I need two CASE LAW related to the case below, NOT an explanation. Thx. (Except Cutter v Powell (1795), and Re Moore and Landauer (1921))

Case 7 - Discharge of Contract On 1 October, Shop Improvement Co. was appointed by Swan Cafe to do their cafe renovation. The terms of contract stated that Swan Cafe would pay HK$1.8 million and the whole project must be completed on or before 20 December. Renovation started on 10 October and by 1 December two third of the project had been completed. On 2 December Swan Cafe was informed by Shop Improvement Co. that one of the special machine needed for the renovation work had broken down, they already checked with the machine supplier but no spare part was available and it would take at least 2 months to get the spare part from the UK manufacturer. Shop Improvement Co. said that they would not be able to finish the renovation by 20 December as agreed. They also asked Swan Cafe to pay two third of the agreed contract price because the shortage of spare parts was beyond their control and it was not their fault. Advise Swan Cafe on their legal position