We're dividing 171129 by 42 
Our goal is to divide 171129 by 42.

On to step 1:
1 divided by 42 is 0 with a remainder of 1.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
The remainder is 1 after subtracting 0 from 1.
Bring next digit (7) of the dividend behind the 1 and repeat the process: 17 / 42

Step 2:
42 can be fit into 17 0 times, resulting in a remainder of 17.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we take 0 away from 17, we end up with 17.
Fetch the next digit (1) from the dividend, attach it to 17 and continue: 171 / 42

On to step 3:
If we divide 171 by 42, we get 4 and a remainder of 3.
The number 4 becomes the next digit in our result. 
Result so far: 4.0
Deduct 168 from 171 and we're left with 3.
Take the next digit (1) from the dividend and append it to 3, then repeat: 31 / 42

Let's proceed to step 4:
42 can be fit into 31 0 times, resulting in a remainder of 31.
Write down 0 as next digit of the result. 
Result so far: 40.0
If we subtract 0 from 31, we get 31.
Fetch the next digit (2) from the dividend, attach it to 31 and continue: 312 / 42

Advancing to step 5:
When dividing 312 by 42, we get 7 with a remainder of 18.
Record the quotient 7 as the next digit in the result. 
Result so far: 407.0
Subtract 294 from 312 to get 18.
Include the next digit (9) from the dividend after 18, then repeat: 189 / 42

Step 6:
189 divided by 42 is 4 with a remainder of 21.
Use 4 as the next digit of our solution. 
Result so far: 4074.0
The remainder is 21 after subtracting 168 from 189.
Since there are no more digits in the dividend, we add a zero to the remainder making it 210, and continue the process.

Step 7:
42 goes into 210 5 times with a remainder of 0.
The number 5 becomes the next digit in our result. 
Result so far: 4074.5
Subtract 210 from 210 to get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

On to step 8:
When dividing 0 by 42, we get 0 with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 4074.5
Subtracting 0 from 0 leaves us with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Advancing to step 9:
The number 42 fits into 0 0 times, leaving a remainder of 0.
Write down 0 as next digit of the result. 
Result so far: 4074.5
The remainder is 0 after subtracting 0 from 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

The final result is 4074.5 with a remainder of 0.0.