Okay, let's tackle this math problem. We're starting with 683836 and subtracting 78406.

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

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

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

Step 4: We'll start by subtracting the digit 8 and the borrow 0 from 3 in column 4 and get -5.
We add -5 to 10 and get 5 as the next digit of the result.

Step 5: We'll start by subtracting the digit 7 and the borrow 1 from 8 in column 5 and get 0.
0 is the next digit of our result.

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

So, 683836 - 78406 = 605430.