138800 ÷ 21 
Our goal is to divide 138800 by 21.

On to step 1:
1 divided by 21 is 0 with a remainder of 1.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we take 0 away from 1, we end up with 1.
Bring next digit (3) of the dividend behind the 1 and repeat the process: 13 / 21

Step 2:
21 goes into 13 0 times with a remainder of 13.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we subtract 0 from 13, we get 13.
Bring next digit (8) of the dividend behind the 13 and repeat the process: 138 / 21

Advancing to step 3:
138 divided by 21 is 6 with a remainder of 12.
Write down 6 as next digit of the result. 
Result so far: 6.0
If we subtract 126 from 138, we get 12.
Take the next digit (8) from the dividend and append it to 12, then repeat: 128 / 21

On to step 4:
When dividing 128 by 21, we get 6 with a remainder of 2.
Write down 6 as next digit of the result. 
Result so far: 66.0
Subtracting 126 from 128 leaves us with 2.
Take the next digit (0) from the dividend and append it to 2, then repeat: 20 / 21

Moving on to step 5:
The number 21 fits into 20 0 times, leaving a remainder of 20.
The number 0 becomes the next digit in our result. 
Result so far: 660.0
If we take 0 away from 20, we end up with 20.
Include the next digit (0) from the dividend after 20, then repeat: 200 / 21

Going ahead to step 6:
200 divided by 21 is 9 with a remainder of 11.
Use 9 as the next digit of our solution. 
Result so far: 6609.0
If we take 189 away from 200, we end up 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.

On to step 7:
21 goes into 110 5 times with a remainder of 5.
Use 5 as the next digit of our solution. 
Result so far: 6609.5
If we take 105 away from 110, we end up with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Going ahead to step 8:
If we divide 50 by 21, we get 2 and a remainder of 8.
The next digit of our result is 2. 
Result so far: 6609.52
The remainder is 8 after subtracting 42 from 50.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Moving on to step 9:
When dividing 80 by 21, we get 3 with a remainder of 17.
The next digit of our result is 3. 
Result so far: 6609.523
If we take 63 away from 80, we end up with 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Going ahead to step 10:
When dividing 170 by 21, we get 8 with a remainder of 2.
Put 8 as the next digit of the answer. 
Result so far: 6609.5238
Subtract 168 from 170 to get 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

On to step 11:
20 divided by 21 is 0 with a remainder of 20.
Put 0 as the next digit of the answer. 
Result so far: 6609.5238
If we subtract 0 from 20, we get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Advancing to step 12:
The number 21 fits into 200 9 times, leaving a remainder of 11.
Put 9 as the next digit of the answer. 
Result so far: 6609.523809
If we subtract 189 from 200, we get 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Step 13:
When dividing 110 by 21, we get 5 with a remainder of 5.
Put 5 as the next digit of the answer. 
Result so far: 6609.5238095
If we subtract 105 from 110, we get 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Step 14:
21 can be fit into 50 2 times, resulting in a remainder of 8.
Write down 2 as next digit of the result. 
Result so far: 6609.52380952
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.

Our division results in 6609.52380952 with a remaining 8e-09.