The memory unit of a computer has 256K words of 32 bits each. The computer has an instruction format with 4 fields: an opcode field; a mode field to specify 1 of 7 addressing modes; a register address field to specify 1 of 60 registers; and a memory address field Assume an instruction is 32 bits long. Answer the following: a. How large must the mode field be? How large must the register field be? c. How large must the address field be? d. How large is the opcode field