Okay, let's tackle this math problem. We're starting with 646457 and subtracting 65649.

Step 1: We'll start by subtracting the digit 9 and the borrow 0 from 7 in column 1 and get -2.
We add -2 to 10 and get 8 as the first digit of the result.

Step 2: We'll start by subtracting the digit 4 and the borrow 1 from 5 in column 2 and get 0.
0 is the next digit of our result.

Step 3: We'll start by subtracting the digit 6 and the borrow 0 from 4 in column 3 and get -2.
We add -2 to 10 and get 8 as the next digit of the result.

Step 4: We'll start by subtracting the digit 5 and the borrow 1 from 6 in column 4 and get 0.
0 is the next digit of our result.

Step 5: We'll start by subtracting the digit 6 and the borrow 0 from 4 in column 5 and get -2.
We add -2 to 10 and get 8 as the next digit of the result.

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

So, 646457 - 65649 = 580808.