We're dividing 393451 by 21 
We're looking to find how many times 21 goes into 393451.

Let's proceed to step 1:
21 can be fit into 3 0 times, resulting in a remainder of 3.
The next digit of our result is 0. 
Result so far: 0.0
Subtracting 0 from 3 leaves us with 3.
Bring next digit (9) of the dividend behind the 3 and repeat the process: 39 / 21

Going ahead to step 2:
The number 21 fits into 39 1 times, leaving a remainder of 18.
Record the quotient 1 as the next digit in the result. 
Result so far: 1.0
Subtract 21 from 39 to get 18.
Include the next digit (3) from the dividend after 18, then repeat: 183 / 21

Step 3:
21 goes into 183 8 times with a remainder of 15.
Use 8 as the next digit of our solution. 
Result so far: 18.0
The remainder is 15 after subtracting 168 from 183.
Fetch the next digit (4) from the dividend, attach it to 15 and continue: 154 / 21

Moving on to step 4:
21 goes into 154 7 times with a remainder of 7.
The next digit of our result is 7. 
Result so far: 187.0
The remainder is 7 after subtracting 147 from 154.
Grab the next digit (5) from the dividend, add it to 7, then carry on: 75 / 21

Going ahead to step 5:
When dividing 75 by 21, we get 3 with a remainder of 12.
Use 3 as the next digit of our solution. 
Result so far: 1873.0
The remainder is 12 after subtracting 63 from 75.
Grab the next digit (1) from the dividend, add it to 12, then carry on: 121 / 21

Let's proceed to step 6:
121 divided by 21 is 5 with a remainder of 16.
The number 5 becomes the next digit in our result. 
Result so far: 18735.0
If we take 105 away from 121, we end up 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.

Advancing to step 7:
The number 21 fits into 160 7 times, leaving a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 18735.7
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 8:
130 divided by 21 is 6 with a remainder of 4.
The number 6 becomes the next digit in our result. 
Result so far: 18735.76
If we take 126 away from 130, we end up 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.

Let's proceed to step 9:
40 divided by 21 is 1 with a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 18735.761
If we take 21 away from 40, we end up with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

On to step 10:
21 goes into 190 9 times with a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 18735.7619
If we take 189 away from 190, we end up 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.

Moving on to step 11:
10 divided by 21 is 0 with a remainder of 10.
The number 0 becomes the next digit in our result. 
Result so far: 18735.7619
Subtract 0 from 10 to 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.

Let's proceed to step 12:
The number 21 fits into 100 4 times, leaving a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 18735.761904
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.

Step 13:
21 goes into 160 7 times with a remainder of 13.
Write down 7 as next digit of the result. 
Result so far: 18735.7619047
The remainder is 13 after subtracting 147 from 160.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Going ahead to step 14:
130 divided by 21 is 6 with a remainder of 4.
Record the quotient 6 as the next digit in the result. 
Result so far: 18735.76190476
Deduct 126 from 130 and we're left 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.

The final result is 18735.76190476 with a remainder of 4e-09.