We can solve this together! We're beginning with 55599 and removing 863 from it.

Step 1: We'll start by subtracting the digit 3 and the borrow 0 from 9 in column 1 and get 6.
6 is the first digit of our result.

Step 2: We'll start by subtracting the digit 6 and the borrow 0 from 9 in column 2 and get 3.
3 is the next digit of our result.

Step 3: We'll start by subtracting the digit 8 and the borrow 0 from 5 in column 3 and get -3.
We add -3 to 10 and get 7 as the next digit of the result.

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

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

So, 55599 - 863 = 54736.