Okay, let's tackle this math problem. We're starting with 503899 and subtracting 79750.

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

Step 2: We'll start by subtracting the digit 5 and the borrow 0 from 9 in column 2 and get 4.
4 is the next digit of our result.

Step 3: We'll start by subtracting the digit 7 and the borrow 0 from 8 in column 3 and get 1.
1 is the next digit of our result.

Step 4: We'll start by subtracting the digit 9 and the borrow 0 from 3 in column 4 and get -6.
We add -6 to 10 and get 4 as the next digit of the result.

Step 5: We'll start by subtracting the digit 7 and the borrow 1 from 0 in column 5 and get -8.
We add -8 to 10 and get 2 as the next digit of the result.

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

So, 503899 - 79750 = 424149.