We're dividing 393558 by 21 
We're looking to find how many times 21 goes into 393558.

Let's proceed to step 1:
21 goes into 3 0 times with a remainder of 3.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 3, we end up with 3.
Grab the next digit (9) from the dividend, add it to 3, then carry on: 39 / 21

Moving on to step 2:
21 goes into 39 1 times with a remainder of 18.
Write down 1 as next digit of the result. 
Result so far: 1.0
Subtracting 21 from 39 leaves us with 18.
Append the next digit (3) from the dividend to 18 and continue with: 183 / 21

Going ahead to step 3:
The number 21 fits into 183 8 times, leaving a remainder of 15.
Record the quotient 8 as the next digit in the result. 
Result so far: 18.0
If we take 168 away from 183, we end up with 15.
Bring next digit (5) of the dividend behind the 15 and repeat the process: 155 / 21

Let's proceed to step 4:
The number 21 fits into 155 7 times, leaving a remainder of 8.
The number 7 becomes the next digit in our result. 
Result so far: 187.0
Subtract 147 from 155 to get 8.
Include the next digit (5) from the dividend after 8, then repeat: 85 / 21

On to step 5:
If we divide 85 by 21, we get 4 and a remainder of 1.
The number 4 becomes the next digit in our result. 
Result so far: 1874.0
If we take 84 away from 85, we end up with 1.
Include the next digit (8) from the dividend after 1, then repeat: 18 / 21

Step 6:
When dividing 18 by 21, we get 0 with a remainder of 18.
Use 0 as the next digit of our solution. 
Result so far: 18740.0
If we take 0 away from 18, we end up with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Advancing to step 7:
The number 21 fits into 180 8 times, leaving a remainder of 12.
The next digit of our result is 8. 
Result so far: 18740.8
Subtract 168 from 180 to 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.

Advancing to step 8:
If we divide 120 by 21, we get 5 and a remainder of 15.
Use 5 as the next digit of our solution. 
Result so far: 18740.85
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.

Going ahead to step 9:
150 divided by 21 is 7 with a remainder of 3.
The number 7 becomes the next digit in our result. 
Result so far: 18740.857
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 10:
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: 18740.8571
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.

Moving on to step 11:
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: 18740.85714
The remainder is 6 after subtracting 84 from 90.
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 12:
21 goes into 60 2 times with a remainder of 18.
The next digit of our result is 2. 
Result so far: 18740.857142
Subtracting 42 from 60 leaves us with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Going ahead to step 13:
The number 21 fits into 180 8 times, leaving a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 18740.8571428
If we take 168 away from 180, we end up 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.

Step 14:
120 divided by 21 is 5 with a remainder of 15.
The next digit of our result is 5. 
Result so far: 18740.85714285
Deduct 105 from 120 and we're left 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.

In conclusion, the division gives 18740.85714285 with a balance of 1.5e-08.