Let's dive into this subtraction. We'll start with 74142 and subtract 6646 from it.

Step 1: We'll start by subtracting the digit 6 and the borrow 0 from 2 in column 1 and get -4.
We add -4 to 10 and get 6 as the first digit of the result.

Step 2: We'll start by subtracting the digit 4 and the borrow 1 from 4 in column 2 and get -1.
We add -1 to 10 and get 9 as the next digit of the result.

Step 3: We'll start by subtracting the digit 6 and the borrow 1 from 1 in column 3 and get -6.
We add -6 to 10 and get 4 as the next digit of the result.

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

So, 74142 - 6646 = 67496.