Let's get this math done. We have 142599 and 20402, and we're going to subtract the second number from the first.

Step 1: We'll start by subtracting the digit 2 and the borrow 0 from 9 in column 1 and get 7.
7 is the first digit of our result.

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

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

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

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

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

So, 142599 - 20402 = 122197.