Okay, let's tackle this math problem. We're starting with 42370 and subtracting 2617.

Step 1: We'll start by subtracting the digit 7 and the borrow 0 from 0 in column 1 and get -7.
We add -7 to 10 and get 3 as the first digit of the result.

Step 2: We'll start by subtracting the digit 1 and the borrow 1 from 7 in column 2 and get 5.
5 is the next digit of our result.

Step 3: We'll start by subtracting the digit 6 and the borrow 0 from 3 in column 3 and get -3.
We add -3 to 10 and get 7 as the next digit of the result.

Step 4: We'll start by subtracting the digit 2 and the borrow 1 from 2 in column 4 and get -1.
We add -1 to 10 and get 9 as the next digit of the result.

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

So, 42370 - 2617 = 39753.