Explanation:
When we need to subtract a number from another number, in that case, we can take the complement of the first number to add it to the second number, the result will be the same. It is because when we take the complement of 9 of that number, it will represent the negative of that number. Hence, by adding the negative of a number we will get the same result as we get after subtraction.
For example:
Subtract 213 from 843
843 - 213 = 630
complement of 9 of 213= 999-213
=786
Now, add 786 and 843
786+843=1629
We got the result in 4 digits so by adding the left-most digit to the right-sided three-digit number of the result, we will get
629+1 = 630