Let's get this math done. We have 81861 and 64188, and we're going to subtract the second number from the first.

Step 1: We'll start by subtracting the digit 8 and the borrow 0 from 1 in column 1 and get -7.
We add -7 to 10 and get 3 as the first digit of the result.

Step 2: We'll start by subtracting the digit 8 and the borrow 1 from 6 in column 2 and get -3.
We add -3 to 10 and get 7 as the next digit of the result.

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

Step 4: We'll start by subtracting the digit 4 and the borrow 0 from 1 in column 4 and get -3.
We add -3 to 10 and get 7 as the next digit of the result.

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

So, 81861 - 64188 = 17673.