A series of tool life tests are conducted on the base material (B1112 steel) and the work material (cast aluminium alloy) under identical cutting conditions, only varying speed in test procedure. The cutting tool is made of cemented carbides. The machinability of base material is 1.0 while the machinability of the cast aluminium alloy is 1.25, which is rated using the cutting speed that provides a 60-minute tool life. For the base material, its tool life is 2 hours after running at a cutting speed of 150 m/min and its tool life is 30 hours if the cutting speed is 75 m/min. (c) Determine the tool life of the cast aluminium alloy when the cutting speed is 250 m/min. (d) Determine the cutting speed of the cast aluminium alloy that allows the tool life determined in part (a) when a high-speed steel tool is used.