Let's dive into this subtraction. We'll start with 815860 and subtract 3005 from it.

Step 1: We'll start by subtracting the digit 5 and the borrow 0 from 0 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 0 and the borrow 1 from 6 in column 2 and get 5.
5 is the next digit of our result.

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

Step 4: We'll start by subtracting the digit 3 and the borrow 0 from 5 in column 4 and get 2.
2 is the next digit of our result.

Step 5: We'll start by subtracting the digit 0 and the borrow 0 from 1 in column 5 and get 1.
1 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, 815860 - 3005 = 812855.