OK, let's do this. We've got 819644 and 55989, and we're subtracting the second number from the first.

Step 1: We'll start by subtracting the digit 9 and the borrow 0 from 4 in column 1 and get -5.
We add -5 to 10 and get 5 as the first digit of the result.

Step 2: We'll start by subtracting the digit 8 and the borrow 1 from 4 in column 2 and get -5.
We add -5 to 10 and get 5 as the next digit of the result.

Step 3: We'll start by subtracting the digit 9 and the borrow 1 from 6 in column 3 and get -4.
We add -4 to 10 and get 6 as the next digit of the result.

Step 4: We'll start by subtracting the digit 5 and the borrow 1 from 9 in column 4 and get 3.
3 is the next digit of our result.

Step 5: We'll start by subtracting the digit 5 and the borrow 0 from 1 in column 5 and get -4.
We add -4 to 10 and get 6 as the next digit of the result.

Step 6: We'll start by subtracting the digit 0 and the borrow 1 from 8 in column 6 and get 7.
7 is the next digit of our result.

So, 819644 - 55989 = 763655.