We look at the division of 343456 by 21 
Our goal is to divide 343456 by 21.

Step 1:
When dividing 3 by 21, we get 0 with a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtract 0 from 3 to get 3.
Take the next digit (4) from the dividend and append it to 3, then repeat: 34 / 21

Going ahead to step 2:
If we divide 34 by 21, we get 1 and a remainder of 13.
The next digit of our result is 1. 
Result so far: 1.0
Deduct 21 from 34 and we're left with 13.
Bring next digit (3) of the dividend behind the 13 and repeat the process: 133 / 21

Let's proceed to step 3:
The number 21 fits into 133 6 times, leaving a remainder of 7.
Record the quotient 6 as the next digit in the result. 
Result so far: 16.0
Subtracting 126 from 133 leaves us with 7.
Take the next digit (4) from the dividend and append it to 7, then repeat: 74 / 21

On to step 4:
When dividing 74 by 21, we get 3 with a remainder of 11.
The number 3 becomes the next digit in our result. 
Result so far: 163.0
If we take 63 away from 74, we end up with 11.
Take the next digit (5) from the dividend and append it to 11, then repeat: 115 / 21

Moving on to step 5:
When dividing 115 by 21, we get 5 with a remainder of 10.
Use 5 as the next digit of our solution. 
Result so far: 1635.0
Subtract 105 from 115 to get 10.
Include the next digit (6) from the dividend after 10, then repeat: 106 / 21

Going ahead to step 6:
21 goes into 106 5 times with a remainder of 1.
Write down 5 as next digit of the result. 
Result so far: 16355.0
Deduct 105 from 106 and we're left with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

On to step 7:
21 goes into 10 0 times with a remainder of 10.
The next digit of our result is 0. 
Result so far: 16355.0
If we subtract 0 from 10, we get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Step 8:
The number 21 fits into 100 4 times, leaving a remainder of 16.
The next digit of our result is 4. 
Result so far: 16355.04
Subtracting 84 from 100 leaves us with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

On to step 9:
The number 21 fits into 160 7 times, leaving a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 16355.047
Subtracting 147 from 160 leaves us with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

On to step 10:
The number 21 fits into 130 6 times, leaving a remainder of 4.
Use 6 as the next digit of our solution. 
Result so far: 16355.0476
Subtracting 126 from 130 leaves us with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Moving on to step 11:
When dividing 40 by 21, we get 1 with a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 16355.04761
The remainder is 19 after subtracting 21 from 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Let's proceed to step 12:
When dividing 190 by 21, we get 9 with a remainder of 1.
Use 9 as the next digit of our solution. 
Result so far: 16355.047619
If we subtract 189 from 190, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Advancing to step 13:
The number 21 fits into 10 0 times, leaving a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 16355.047619
Deduct 0 from 10 and we're left with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Moving on to step 14:
When dividing 100 by 21, we get 4 with a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 16355.04761904
If we subtract 84 from 100, we get 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

The final outcome is 16355.04761904, with a leftover of 1.6e-08.