We can solve this together! We're beginning with 99399 and removing 56901 from it.

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 0 and the borrow 0 from 9 in column 2 and get 9.
9 is the next digit of our result.

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

Step 4: We'll start by subtracting the digit 6 and the borrow 1 from 9 in column 4 and get 2.
2 is the next digit of our result.

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

So, 99399 - 56901 = 42498.