309787 divided by 21 
Let's see how many times 21 fits into 309787.

Moving on to step 1:
The number 21 fits into 3 0 times, leaving 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.
Append the next digit (0) from the dividend to 3 and continue with: 30 / 21

Step 2:
The number 21 fits into 30 1 times, leaving a remainder of 9.
The next digit of our result is 1. 
Result so far: 1.0
The remainder is 9 after subtracting 21 from 30.
Grab the next digit (9) from the dividend, add it to 9, then carry on: 99 / 21

Let's proceed to step 3:
When dividing 99 by 21, we get 4 with a remainder of 15.
Use 4 as the next digit of our solution. 
Result so far: 14.0
The remainder is 15 after subtracting 84 from 99.
Take the next digit (7) from the dividend and append it to 15, then repeat: 157 / 21

Step 4:
21 goes into 157 7 times with a remainder of 10.
The number 7 becomes the next digit in our result. 
Result so far: 147.0
If we subtract 147 from 157, we get 10.
Fetch the next digit (8) from the dividend, attach it to 10 and continue: 108 / 21

Step 5:
108 divided by 21 is 5 with a remainder of 3.
The next digit of our result is 5. 
Result so far: 1475.0
Subtract 105 from 108 to get 3.
Grab the next digit (7) from the dividend, add it to 3, then carry on: 37 / 21

Let's proceed to step 6:
If we divide 37 by 21, we get 1 and a remainder of 16.
Write down 1 as next digit of the result. 
Result so far: 14751.0
Deduct 21 from 37 and we're left 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 7:
21 goes into 160 7 times with a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 14751.7
Subtract 147 from 160 to get 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Moving on to step 8:
21 can be fit into 130 6 times, resulting in a remainder of 4.
Use 6 as the next digit of our solution. 
Result so far: 14751.76
Subtract 126 from 130 to get 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Step 9:
If we divide 40 by 21, we get 1 and a remainder of 19.
The number 1 becomes the next digit in our result. 
Result so far: 14751.761
The remainder is 19 after subtracting 21 from 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Advancing to step 10:
190 divided by 21 is 9 with a remainder of 1.
Use 9 as the next digit of our solution. 
Result so far: 14751.7619
Deduct 189 from 190 and we're left 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.

Going ahead to step 11:
21 goes into 10 0 times with a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 14751.7619
If we subtract 0 from 10, we 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.

On to step 12:
The number 21 fits into 100 4 times, leaving a remainder of 16.
Use 4 as the next digit of our solution. 
Result so far: 14751.761904
If we take 84 away from 100, 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 13:
21 goes into 160 7 times with a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 14751.7619047
If we subtract 147 from 160, we get 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Moving on to step 14:
21 can be fit into 130 6 times, resulting in a remainder of 4.
Use 6 as the next digit of our solution. 
Result so far: 14751.76190476
Subtracting 126 from 130 leaves us 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 14751.76190476 with a remainder of 4e-09.