We look at the division of 339573 by 21 
We're looking to find how many times 21 goes into 339573.

Moving on to step 1:
21 goes into 3 0 times with a remainder of 3.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 3, we get 3.
Include the next digit (3) from the dividend after 3, then repeat: 33 / 21

Going ahead to step 2:
33 divided by 21 is 1 with a remainder of 12.
Record the quotient 1 as the next digit in the result. 
Result so far: 1.0
The remainder is 12 after subtracting 21 from 33.
Include the next digit (9) from the dividend after 12, then repeat: 129 / 21

Let's proceed to step 3:
21 goes into 129 6 times with a remainder of 3.
Record the quotient 6 as the next digit in the result. 
Result so far: 16.0
Subtract 126 from 129 to get 3.
Grab the next digit (5) from the dividend, add it to 3, then carry on: 35 / 21

Step 4:
21 goes into 35 1 times with a remainder of 14.
The next digit of our result is 1. 
Result so far: 161.0
Subtract 21 from 35 to get 14.
Grab the next digit (7) from the dividend, add it to 14, then carry on: 147 / 21

Let's proceed to step 5:
If we divide 147 by 21, we get 7 and a remainder of 0.
Record the quotient 7 as the next digit in the result. 
Result so far: 1617.0
Subtract 147 from 147 to get 0.
Fetch the next digit (3) from the dividend, attach it to 0 and continue: 3 / 21

Going ahead to step 6:
21 goes into 3 0 times with a remainder of 3.
The next digit of our result is 0. 
Result so far: 16170.0
Subtract 0 from 3 to get 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Advancing to step 7:
If we divide 30 by 21, we get 1 and a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 16170.1
If we subtract 21 from 30, we get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

On to step 8:
When dividing 90 by 21, we get 4 with a remainder of 6.
Use 4 as the next digit of our solution. 
Result so far: 16170.14
If we subtract 84 from 90, we get 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Step 9:
The number 21 fits into 60 2 times, leaving a remainder of 18.
Use 2 as the next digit of our solution. 
Result so far: 16170.142
If we subtract 42 from 60, we get 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Moving on to step 10:
180 divided by 21 is 8 with a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 16170.1428
If we subtract 168 from 180, we get 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Let's proceed to step 11:
If we divide 120 by 21, we get 5 and a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 16170.14285
If we take 105 away from 120, we end up with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

On to step 12:
If we divide 150 by 21, we get 7 and a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 16170.142857
Subtracting 147 from 150 leaves us with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Step 13:
When dividing 30 by 21, we get 1 with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 16170.1428571
Subtract 21 from 30 to get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Moving on to step 14:
If we divide 90 by 21, we get 4 and a remainder of 6.
Write down 4 as next digit of the result. 
Result so far: 16170.14285714
If we take 84 away from 90, we end up with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Our division results in 16170.14285714 with a remaining 6e-09.