Alright, ready to do some subtraction? We're taking 199790 and subtracting 40645 from it.

Step 1: We'll start by subtracting the digit 5 and the borrow 0 from 0 in column 1 and get -5.
We add -5 to 10 and get 5 as the first digit of the result.

Step 2: We'll start by subtracting the digit 4 and the borrow 1 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 6 and the borrow 0 from 7 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 9 in column 4 and get 9.
9 is the next digit of our result.

Step 5: We'll start by subtracting the digit 4 and the borrow 0 from 9 in column 5 and get 5.
5 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, 199790 - 40645 = 159145.