We're dividing 17989 by 21 
We're looking to find how many times 21 goes into 17989.

Going ahead to step 1:
21 goes into 1 0 times with a remainder of 1.
Use 0 as the next digit of our solution. 
Result so far: 0.0
The remainder is 1 after subtracting 0 from 1.
Grab the next digit (7) from the dividend, add it to 1, then carry on: 17 / 21

On to step 2:
21 can be fit into 17 0 times, resulting in a remainder of 17.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we subtract 0 from 17, we get 17.
Bring next digit (9) of the dividend behind the 17 and repeat the process: 179 / 21

Let's proceed to step 3:
The number 21 fits into 179 8 times, leaving a remainder of 11.
The number 8 becomes the next digit in our result. 
Result so far: 8.0
Deduct 168 from 179 and we're left with 11.
Take the next digit (8) from the dividend and append it to 11, then repeat: 118 / 21

Step 4:
If we divide 118 by 21, we get 5 and a remainder of 13.
Use 5 as the next digit of our solution. 
Result so far: 85.0
The remainder is 13 after subtracting 105 from 118.
Include the next digit (9) from the dividend after 13, then repeat: 139 / 21

On to step 5:
The number 21 fits into 139 6 times, leaving a remainder of 13.
Write down 6 as next digit of the result. 
Result so far: 856.0
Subtract 126 from 139 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 6:
130 divided by 21 is 6 with a remainder of 4.
The number 6 becomes the next digit in our result. 
Result so far: 856.6
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.

On to step 7:
The number 21 fits into 40 1 times, leaving a remainder of 19.
The next digit of our result is 1. 
Result so far: 856.61
Subtract 21 from 40 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Going ahead to step 8:
190 divided by 21 is 9 with a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 856.619
The remainder is 1 after subtracting 189 from 190.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Moving on to step 9:
When dividing 10 by 21, we get 0 with a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 856.619
The remainder is 10 after subtracting 0 from 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Moving on to step 10:
When dividing 100 by 21, we get 4 with a remainder of 16.
Use 4 as the next digit of our solution. 
Result so far: 856.61904
Deduct 84 from 100 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.

Going ahead to step 11:
When dividing 160 by 21, we get 7 with a remainder of 13.
The next digit of our result is 7. 
Result so far: 856.619047
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.

Going ahead to step 12:
The number 21 fits into 130 6 times, leaving a remainder of 4.
The next digit of our result is 6. 
Result so far: 856.6190476
If we subtract 126 from 130, we 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.

Advancing to step 13:
40 divided by 21 is 1 with a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 856.61904761
Subtract 21 from 40 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

The final outcome is 856.61904761, with a leftover of 1.9e-08.