345204 ÷ 21 
Our goal is to divide 345204 by 21.

Moving on to step 1:
When dividing 3 by 21, we get 0 with a remainder of 3.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtracting 0 from 3 leaves us with 3.
Include the next digit (4) from the dividend after 3, then repeat: 34 / 21

On to step 2:
The number 21 fits into 34 1 times, leaving a remainder of 13.
Put 1 as the next digit of the answer. 
Result so far: 1.0
Subtracting 21 from 34 leaves us with 13.
Fetch the next digit (5) from the dividend, attach it to 13 and continue: 135 / 21

Advancing to step 3:
The number 21 fits into 135 6 times, leaving a remainder of 9.
Put 6 as the next digit of the answer. 
Result so far: 16.0
Deduct 126 from 135 and we're left with 9.
Bring next digit (2) of the dividend behind the 9 and repeat the process: 92 / 21

Let's proceed to step 4:
If we divide 92 by 21, we get 4 and a remainder of 8.
Use 4 as the next digit of our solution. 
Result so far: 164.0
Subtract 84 from 92 to get 8.
Bring next digit (0) of the dividend behind the 8 and repeat the process: 80 / 21

Step 5:
80 divided by 21 is 3 with a remainder of 17.
The next digit of our result is 3. 
Result so far: 1643.0
If we take 63 away from 80, we end up with 17.
Append the next digit (4) from the dividend to 17 and continue with: 174 / 21

Going ahead to step 6:
When dividing 174 by 21, we get 8 with a remainder of 6.
Use 8 as the next digit of our solution. 
Result so far: 16438.0
If we take 168 away from 174, 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.

Going ahead to step 7:
When dividing 60 by 21, we get 2 with a remainder of 18.
Write down 2 as next digit of the result. 
Result so far: 16438.2
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 8:
When dividing 180 by 21, we get 8 with a remainder of 12.
Put 8 as the next digit of the answer. 
Result so far: 16438.28
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.

Going ahead to step 9:
When dividing 120 by 21, we get 5 with a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 16438.285
If we subtract 105 from 120, we get 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Going ahead to step 10:
If we divide 150 by 21, we get 7 and a remainder of 3.
The next digit of our result is 7. 
Result so far: 16438.2857
If we take 147 away from 150, we end up 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.

Advancing to step 11:
The number 21 fits into 30 1 times, leaving a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 16438.28571
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.

Step 12:
90 divided by 21 is 4 with a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 16438.285714
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.

On to step 13:
60 divided by 21 is 2 with a remainder of 18.
Put 2 as the next digit of the answer. 
Result so far: 16438.2857142
Subtract 42 from 60 to 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.

Step 14:
21 goes into 180 8 times with a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 16438.28571428
Subtracting 168 from 180 leaves us with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Our division results in 16438.28571428 with a remaining 1.2e-08.