Convert given base-10 numbers, (342)10 and (173)10, to base-8 using remainder method.
342÷8=42 R6, 42÷8=5 R2, 5÷8=0 R5, so (342)10=(526)8
173÷8=21 R5, 21÷8=2 R5, 2÷8=0 R2, so (173)10=(255)8
Thus, (342)10-173(10)=(526)8-(255)8
* Expand (526)8, (255)8 with power of 8, using the fact that each place in a base-8 number represents a power of 8.
(526)8=5x8²+2x8¹+6x8º=(5-1)x8²+(8+2)x8¹+6x8º, and (255)8=2x8²+5x8¹+5x8º
We have: (526)8-(255)8=(5-1-2)x8²+(8+2-5)x8¹+(6-5)x8º=2x8²+5x8¹+1x8º
** That is: (526)8-(255)8=(251)8
CK: (251)8=2x8²+5x8¹+1x8º=128+40+1=(169)10=(342)10-(173)10 CKD.
The answer is: (342)10-(173)10=(526)8-(255)8=(251)8
* If you familia with borrowing in base-8 subtraction, just skip this part and go to **.