Let's dive into this subtraction. We'll start with 84278 and subtract 68378 from it.

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

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

Step 3: We'll start by subtracting the digit 3 and the borrow 0 from 2 in column 3 and get -1.
We add -1 to 10 and get 9 as the next digit of the result.

Step 4: We'll start by subtracting the digit 8 and the borrow 1 from 4 in column 4 and get -5.
We add -5 to 10 and get 5 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, 84278 - 68378 = 15900.