OK, let's do this. We've got 878989 and 23386, and we're subtracting the second number from the first.

Step 1: We'll start by subtracting the digit 6 and the borrow 0 from 9 in column 1 and get 3.
3 is the first digit of our result.

Step 2: We'll start by subtracting the digit 8 and the borrow 0 from 8 in column 2 and get 0.
0 is the next digit of our result.

Step 3: We'll start by subtracting the digit 3 and the borrow 0 from 9 in column 3 and get 6.
6 is the next digit of our result.

Step 4: We'll start by subtracting the digit 3 and the borrow 0 from 8 in column 4 and get 5.
5 is the next digit of our result.

Step 5: We'll start by subtracting the digit 2 and the borrow 0 from 7 in column 5 and get 5.
5 is the next digit of our result.

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

So, 878989 - 23386 = 855603.