Let's dive into this subtraction. We'll start with 91017 and subtract 47979 from it.

Step 1: We'll start by subtracting the digit 9 and the borrow 0 from 7 in column 1 and get -2.
We add -2 to 10 and get 8 as the first digit of the result.

Step 2: We'll start by subtracting the digit 7 and the borrow 1 from 1 in column 2 and get -7.
We add -7 to 10 and get 3 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 7 and the borrow 1 from 1 in column 4 and get -7.
We add -7 to 10 and get 3 as the next digit of the result.

Step 5: We'll start by subtracting the digit 4 and the borrow 1 from 9 in column 5 and get 4.
4 is the next digit of our result.

So, 91017 - 47979 = 43038.