OK, let's do this. We've got 31079 and 20997, and we're subtracting the second number from the first.

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

Step 2: We'll start by subtracting the digit 9 and the borrow 0 from 7 in column 2 and get -2.
We add -2 to 10 and get 8 as the next digit of the result.

Step 3: We'll start by subtracting the digit 9 and the borrow 1 from 0 in column 3 and get -10.
We add -10 to 10 and get 0 as the next digit of the result.

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

Step 5: We'll start by subtracting the digit 2 and the borrow 0 from 3 in column 5 and get 1.
1 is the next digit of our result.

So, 31079 - 20997 = 10082.