Let's divide 399154 by 21
We want to divide 399154 by 21.

Step 1:
21 can be fit into 3 0 times, resulting in a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we take 0 away from 3, we end up with 3.
Fetch the next digit (9) from the dividend, attach it to 3 and continue: 39 / 21

Advancing to step 2:
21 can be fit into 39 1 times, resulting in a remainder of 18.
Write down 1 as next digit of the result. 
Result so far: 1.0
Subtract 21 from 39 to get 18.
Include the next digit (9) from the dividend after 18, then repeat: 189 / 21

Step 3:
21 goes into 189 9 times with a remainder of 0.
The number 9 becomes the next digit in our result. 
Result so far: 19.0
The remainder is 0 after subtracting 189 from 189.
Fetch the next digit (1) from the dividend, attach it to 0 and continue: 1 / 21

Going ahead to step 4:
When dividing 1 by 21, we get 0 with a remainder of 1.
Put 0 as the next digit of the answer. 
Result so far: 190.0
If we subtract 0 from 1, we get 1.
Take the next digit (5) from the dividend and append it to 1, then repeat: 15 / 21

Moving on to step 5:
When dividing 15 by 21, we get 0 with a remainder of 15.
Use 0 as the next digit of our solution. 
Result so far: 1900.0
Deduct 0 from 15 and we're left with 15.
Fetch the next digit (4) from the dividend, attach it to 15 and continue: 154 / 21

Step 6:
21 goes into 154 7 times with a remainder of 7.
The number 7 becomes the next digit in our result. 
Result so far: 19007.0
Deduct 147 from 154 and we're left with 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Going ahead to step 7:
70 divided by 21 is 3 with a remainder of 7.
Use 3 as the next digit of our solution. 
Result so far: 19007.3
If we subtract 63 from 70, we get 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Let's proceed to step 8:
If we divide 70 by 21, we get 3 and a remainder of 7.
Record the quotient 3 as the next digit in the result. 
Result so far: 19007.33
If we take 63 away from 70, we end up with 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

After the division, we end up with 19007.33 and a remainder of 0.007.