We're dividing 903809 by 21 
We want to figure out the number of times 903809 can be divided by 21.

Going ahead to step 1:
The number 21 fits into 9 0 times, leaving a remainder of 9.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtract 0 from 9 to get 9.
Grab the next digit (0) from the dividend, add it to 9, then carry on: 90 / 21

Moving on to step 2:
The number 21 fits into 90 4 times, leaving a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 4.0
Deduct 84 from 90 and we're left with 6.
Grab the next digit (3) from the dividend, add it to 6, then carry on: 63 / 21

Advancing to step 3:
The number 21 fits into 63 3 times, leaving a remainder of 0.
Put 3 as the next digit of the answer. 
Result so far: 43.0
Deduct 63 from 63 and we're left with 0.
Include the next digit (8) from the dividend after 0, then repeat: 8 / 21

Moving on to step 4:
8 divided by 21 is 0 with a remainder of 8.
Record the quotient 0 as the next digit in the result. 
Result so far: 430.0
Deduct 0 from 8 and we're left with 8.
Take the next digit (0) from the dividend and append it to 8, then repeat: 80 / 21

On to step 5:
If we divide 80 by 21, we get 3 and a remainder of 17.
Put 3 as the next digit of the answer. 
Result so far: 4303.0
Deduct 63 from 80 and we're left with 17.
Append the next digit (9) from the dividend to 17 and continue with: 179 / 21

Let's proceed to step 6:
21 goes into 179 8 times with a remainder of 11.
Use 8 as the next digit of our solution. 
Result so far: 43038.0
Deduct 168 from 179 and we're left with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Going ahead to step 7:
21 can be fit into 110 5 times, resulting in a remainder of 5.
Record the quotient 5 as the next digit in the result. 
Result so far: 43038.5
The remainder is 5 after subtracting 105 from 110.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Moving on to step 8:
The number 21 fits into 50 2 times, leaving a remainder of 8.
Put 2 as the next digit of the answer. 
Result so far: 43038.52
If we subtract 42 from 50, we get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Step 9:
The number 21 fits into 80 3 times, leaving a remainder of 17.
Use 3 as the next digit of our solution. 
Result so far: 43038.523
If we subtract 63 from 80, we get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Advancing to step 10:
If we divide 170 by 21, we get 8 and a remainder of 2.
Record the quotient 8 as the next digit in the result. 
Result so far: 43038.5238
The remainder is 2 after subtracting 168 from 170.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Step 11:
21 goes into 20 0 times with a remainder of 20.
The next digit of our result is 0. 
Result so far: 43038.5238
Deduct 0 from 20 and we're left with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Step 12:
If we divide 200 by 21, we get 9 and a remainder of 11.
Use 9 as the next digit of our solution. 
Result so far: 43038.523809
Subtracting 189 from 200 leaves us with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Let's proceed to step 13:
110 divided by 21 is 5 with a remainder of 5.
Record the quotient 5 as the next digit in the result. 
Result so far: 43038.5238095
The remainder is 5 after subtracting 105 from 110.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Moving on to step 14:
The number 21 fits into 50 2 times, leaving a remainder of 8.
The next digit of our result is 2. 
Result so far: 43038.52380952
If we subtract 42 from 50, we get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

In conclusion, the division gives 43038.52380952 with a balance of 8e-09.