Alright, ready to do some subtraction? We're taking 78143 and subtracting 12421 from it.

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

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

Step 3: We'll start by subtracting the digit 4 and the borrow 0 from 1 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 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 1 and the borrow 0 from 7 in column 5 and get 6.
6 is the next digit of our result.

So, 78143 - 12421 = 65722.