Hex subtraction again
Why is $4 - $7 = $D with a borrow of 1? The borrow has a weight equal to the BASE (in this case 16). BORROW +$4 - $7 = 16 + 4 -7 = 20 -7 = 13 = $D.
$D is the result of the subtraction with the borrow.
Exactly the same thing happens in decimal. 3 - 8 = 5 with borrow of 1 borrow + 3 - 8 = 10 + 3 - 8 = 13 - 8 = 5.