We can solve this together! We're beginning with 999158 and removing 17780 from it.

Step 1: We'll start by subtracting the digit 0 and the borrow 0 from 8 in column 1 and get 8.
8 is the first digit of our result.

Step 2: We'll start by subtracting the digit 8 and the borrow 0 from 5 in column 2 and get -3.
We add -3 to 10 and get 7 as the next digit of the result.

Step 3: We'll start by subtracting the digit 7 and the borrow 1 from 1 in column 3 and get -7.
We add -7 to 10 and get 3 as the next digit of the result.

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

Step 5: We'll start by subtracting the digit 1 and the borrow 0 from 9 in column 5 and get 8.
8 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, 999158 - 17780 = 981378.