First subtract the ones
6 - 1 = 5 without even having to borrow. But when we go to the next column, which is the eight's column in base 8, we are trying to take away more than we have so we have to borrow. But when we go to the next column to borrow, there is nothing there, so we must go to the next column after that. We borrow one of the five hundred twelves which is eight sixty-fours.
We can now borrow one of the sixty-fours leaving us with 7 in the sixty-four's column, giving us eight eights.
We can now finish the problem. From the table, 7 from 14 is 5, and the rest of the places will not need further borrowing.