850509 ÷ 21 
We want to figure out the number of times 850509 can be divided by 21.

Step 1:
21 can be fit into 8 0 times, resulting in a remainder of 8.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 8 to get 8.
Grab the next digit (5) from the dividend, add it to 8, then carry on: 85 / 21

Let's proceed to step 2:
When dividing 85 by 21, we get 4 with a remainder of 1.
Use 4 as the next digit of our solution. 
Result so far: 4.0
Subtract 84 from 85 to get 1.
Include the next digit (0) from the dividend after 1, then repeat: 10 / 21

Moving on to step 3:
If we divide 10 by 21, we get 0 and a remainder of 10.
The number 0 becomes the next digit in our result. 
Result so far: 40.0
Subtracting 0 from 10 leaves us with 10.
Take the next digit (5) from the dividend and append it to 10, then repeat: 105 / 21

Moving on to step 4:
21 goes into 105 5 times with a remainder of 0.
Put 5 as the next digit of the answer. 
Result so far: 405.0
Subtracting 105 from 105 leaves us with 0.
Take the next digit (0) from the dividend and append it to 0, then repeat: 0 / 21

Advancing to step 5:
If we divide 0 by 21, we get 0 and a remainder of 0.
The next digit of our result is 0. 
Result so far: 4050.0
Subtract 0 from 0 to get 0.
Bring next digit (9) of the dividend behind the 0 and repeat the process: 9 / 21

On to step 6:
When dividing 9 by 21, we get 0 with a remainder of 9.
Put 0 as the next digit of the answer. 
Result so far: 40500.0
The remainder is 9 after subtracting 0 from 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 7:
21 goes into 90 4 times with a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 40500.4
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.

Moving on to step 8:
When dividing 60 by 21, we get 2 with a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 40500.42
Subtract 42 from 60 to get 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Moving on to step 9:
180 divided by 21 is 8 with a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 40500.428
The remainder is 12 after subtracting 168 from 180.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

On to step 10:
120 divided by 21 is 5 with a remainder of 15.
The next digit of our result is 5. 
Result so far: 40500.4285
Subtract 105 from 120 to get 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 11:
If we divide 150 by 21, we get 7 and a remainder of 3.
Record the quotient 7 as the next digit in the result. 
Result so far: 40500.42857
If we subtract 147 from 150, we get 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Let's proceed to step 12:
21 goes into 30 1 times with a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 40500.428571
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 13:
21 can be fit into 90 4 times, resulting in a remainder of 6.
Use 4 as the next digit of our solution. 
Result so far: 40500.4285714
Subtract 84 from 90 to get 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Moving on to step 14:
If we divide 60 by 21, we get 2 and a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 40500.42857142
Deduct 42 from 60 and we're left 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.

The final outcome is 40500.42857142, with a leftover of 1.8e-08.