Okay, let's tackle this math problem. We're starting with 901799 and subtracting 13689.

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

Step 2: We'll start by subtracting the digit 8 and the borrow 0 from 9 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 7 in column 3 and get 1.
1 is the next digit of our result.

Step 4: We'll start by subtracting the digit 3 and the borrow 0 from 1 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 1 and the borrow 1 from 0 in column 5 and get -2.
We add -2 to 10 and get 8 as the next digit of the result.

Step 6: We'll start by subtracting the digit 0 and the borrow 1 from 9 in column 6 and get 8.
8 is the next digit of our result.

So, 901799 - 13689 = 888110.