Figure 1 shows how to use the 74ALS138 3 to 8 lines decoder to decode an 8-bit I/O address into 2 ports. a) Is memory-mapped or isolated I/O used in Figure 1 ? Why? (4 marks) b) Is fixed port or variable port address is used in Figure1? (4 marks) c) Show how to obtain the address of each port. (7 marks)