Okay, let's tackle this math problem. We're starting with 878617 and subtracting 72997.

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

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

Step 3: We'll start by subtracting the digit 9 and the borrow 1 from 6 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 2 and the borrow 1 from 8 in column 4 and get 5.
5 is the next digit of our result.

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

Step 6: We'll start by subtracting the digit 0 and the borrow 0 from 8 in column 6 and get 8.
8 is the next digit of our result.

So, 878617 - 72997 = 805620.