Let's dive into this subtraction. We'll start with 66998 and subtract 7458 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 5 and the borrow 0 from 9 in column 2 and get 4.
4 is the next digit of our result.

Step 3: We'll start by subtracting the digit 4 and the borrow 0 from 9 in column 3 and get 5.
5 is the next digit of our result.

Step 4: We'll start by subtracting the digit 7 and the borrow 0 from 6 in column 4 and get -1.
We add -1 to 10 and get 9 as the next digit of the result.

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

So, 66998 - 7458 = 59540.