Okay, let's tackle this math problem. We're starting with 939152 and subtracting 21900.

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

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

Step 3: We'll start by subtracting the digit 9 and the borrow 0 from 1 in column 3 and get -8.
We add -8 to 10 and get 2 as the next digit of the result.

Step 4: We'll start by subtracting the digit 1 and the borrow 1 from 9 in column 4 and get 7.
7 is the next digit of our result.

Step 5: We'll start by subtracting the digit 2 and the borrow 0 from 3 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 9 in column 6 and get 9.
9 is the next digit of our result.

So, 939152 - 21900 = 917252.