Let's get this math done. We have 751704990 and 87230028, and we're going to subtract the second number from the first.

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

Step 2: We'll start by subtracting the digit 2 and the borrow 1 from 9 in column 2 and get 6.
6 is the next digit of our result.

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

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

Step 5: We'll start by subtracting the digit 3 and the borrow 0 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 2 and the borrow 1 from 7 in column 6 and get 4.
4 is the next digit of our result.

Step 7: We'll start by subtracting the digit 7 and the borrow 0 from 1 in column 7 and get -6.
We add -6 to 10 and get 4 as the next digit of the result.

Step 8: We'll start by subtracting the digit 8 and the borrow 1 from 5 in column 8 and get -4.
We add -4 to 10 and get 6 as the next digit of the result.

Step 9: We'll start by subtracting the digit 0 and the borrow 1 from 7 in column 9 and get 6.
6 is the next digit of our result.

So, 751704990 - 87230028 = 664474962.