Okay, let's tackle this math problem. We're starting with 495900 and subtracting 20793.

Step 1: We'll start by subtracting the digit 3 and the borrow 0 from 0 in column 1 and get -3.
We add -3 to 10 and get 7 as the first digit of the result.

Step 2: We'll start by subtracting the digit 9 and the borrow 1 from 0 in column 2 and get -10.
We add -10 to 10 and get 0 as the next digit of the result.

Step 3: We'll start by subtracting the digit 7 and the borrow 1 from 9 in column 3 and get 1.
1 is the next digit of our result.

Step 4: We'll start by subtracting the digit 0 and the borrow 0 from 5 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 9 in column 5 and get 7.
7 is the next digit of our result.

Step 6: We'll start by subtracting the digit 0 and the borrow 0 from 4 in column 6 and get 4.
4 is the next digit of our result.

So, 495900 - 20793 = 475107.