A digital computer has a memory unit with 30 bits per cell. Each instruction on this computer is 15-bits divided as 4 bits for Opcode and 11 bits for the operand direct address part. Two instructions are packed in one memory word. The computer has the following registers: MAR (11-bits), MDR (30-bits) and IR (30-bits). Write a procedure in your own words for fetching and executing instructions for this computer.