Alright, let's solve this problem step by step. We have 343993 and 490, and we're subtracting the second number from the first.

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

Step 2: We'll start by subtracting the digit 9 and the borrow 0 from 9 in column 2 and get 0.
0 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 0 and the borrow 0 from 3 in column 4 and get 3.
3 is the next digit of our result.

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

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

So, 343993 - 490 = 343503.