Okay, let's tackle this math problem. We're starting with 900376 and subtracting 28864.

Step 1: We'll start by subtracting the digit 4 and the borrow 0 from 6 in column 1 and get 2.
2 is the first digit of our result.

Step 2: We'll start by subtracting the digit 6 and the borrow 0 from 7 in column 2 and get 1.
1 is the next digit of our result.

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

Step 4: We'll start by subtracting the digit 8 and the borrow 1 from 0 in column 4 and get -9.
We add -9 to 10 and get 1 as the next digit of the result.

Step 5: We'll start by subtracting the digit 2 and the borrow 1 from 0 in column 5 and get -3.
We add -3 to 10 and get 7 as the next digit of the result.

Step 6: We'll start by subtracting the digit 0 and the borrow 1 from 9 in column 6 and get 8.
8 is the next digit of our result.

So, 900376 - 28864 = 871512.