4. (30 pts) MIPS assembly language instructions. For each MIPS assembly language instruction given below: Determine the instruction type (R, I, or J), and the decimal value of each field of the instruction. Do not leave any field of the instruction blank. Specify the MIPS machine language instruction in binary and hexadecimal. Briefly describe the function of the instruction. a. (a) Ibu $s4, 17($tl) b. (b) addi $t2, $s4, -9