Let's dive into this subtraction. We'll start with 40239 and subtract 21622 from it.

Step 1: We'll start by subtracting the digit 2 and the borrow 0 from 9 in column 1 and get 7.
7 is the first digit of our result.

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

Step 3: We'll start by subtracting the digit 6 and the borrow 0 from 2 in column 3 and get -4.
We add -4 to 10 and get 6 as the next digit of the result.

Step 4: We'll start by subtracting the digit 1 and the borrow 1 from 0 in column 4 and get -2.
We add -2 to 10 and get 8 as the next digit of the result.

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

So, 40239 - 21622 = 18617.