Got it! So, we have 89977 and 71820, and we'll subtract the latter from the former.

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

Step 3: We'll start by subtracting the digit 8 and the borrow 0 from 9 in column 3 and get 1.
1 is the next digit of our result.

Step 4: We'll start by subtracting the digit 1 and the borrow 0 from 9 in column 4 and get 8.
8 is the next digit of our result.

Step 5: We'll start by subtracting the digit 7 and the borrow 0 from 8 in column 5 and get 1.
1 is the next digit of our result.

So, 89977 - 71820 = 18157.