Okay, let's tackle this math problem. We're starting with 662124 and subtracting 15209.

Step 1: We'll start by subtracting the digit 9 and the borrow 0 from 4 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 2 in column 2 and get 1.
1 is the next digit of our result.

Step 3: We'll start by subtracting the digit 2 and the borrow 0 from 1 in column 3 and get -1.
We add -1 to 10 and get 9 as the next digit of the result.

Step 4: We'll start by subtracting the digit 5 and the borrow 1 from 2 in column 4 and get -4.
We add -4 to 10 and get 6 as the next digit of the result.

Step 5: We'll start by subtracting the digit 1 and the borrow 1 from 6 in column 5 and get 4.
4 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, 662124 - 15209 = 646915.