Alright, let's solve this problem step by step. We have 993410 and 21009, and we're subtracting the second number from the first.

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

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

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

Step 4: We'll start by subtracting the digit 1 and the borrow 0 from 3 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 9 in column 5 and get 7.
7 is the next digit of our result.

Step 6: We'll start by subtracting the digit 0 and the borrow 0 from 9 in column 6 and get 9.
9 is the next digit of our result.

So, 993410 - 21009 = 972401.