Let's get this math done. We have 78398 and 63643, and we're going to subtract the second number from the first.

Step 1: We'll start by subtracting the digit 3 and the borrow 0 from 8 in column 1 and get 5.
5 is the first digit of our result.

Step 2: We'll start by subtracting the digit 4 and the borrow 0 from 9 in column 2 and get 5.
5 is the next digit of our result.

Step 3: We'll start by subtracting the digit 6 and the borrow 0 from 3 in column 3 and get -3.
We add -3 to 10 and get 7 as the next digit of the result.

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

Step 5: We'll start by subtracting the digit 6 and the borrow 0 from 7 in column 5 and get 1.
1 is the next digit of our result.

So, 78398 - 63643 = 14755.