Let's get this math done. We have 999991029 and 75131021, and we're going to subtract the second number from the first.

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

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

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

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

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

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

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

Step 8: We'll start by subtracting the digit 7 and the borrow 0 from 9 in column 8 and get 2.
2 is the next digit of our result.

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

So, 999991029 - 75131021 = 924860008.