First, write for each decimal equivalent binary code :
since 8 = 23
write each digit in 3-bit binary
(342)8 = (011 100 010)2 ignore initial zero
(342)8 = (226)10 = (11100010)2
since all processor use 2's complement number system(2's complement number system is weighted number system)
so 11100010 is a negative number
11100010 = 100010 = -25 + 2 = -30
correct answer D