We look at the division of 80142 by 21 
Let's see how many times 21 fits into 80142.

Let's proceed to step 1:
When dividing 8 by 21, we get 0 with a remainder of 8.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 8, we end up with 8.
Take the next digit (0) from the dividend and append it to 8, then repeat: 80 / 21

On to step 2:
If we divide 80 by 21, we get 3 and a remainder of 17.
The number 3 becomes the next digit in our result. 
Result so far: 3.0
If we subtract 63 from 80, we get 17.
Take the next digit (1) from the dividend and append it to 17, then repeat: 171 / 21

Let's proceed to step 3:
If we divide 171 by 21, we get 8 and a remainder of 3.
Write down 8 as next digit of the result. 
Result so far: 38.0
Deduct 168 from 171 and we're left with 3.
Take the next digit (4) from the dividend and append it to 3, then repeat: 34 / 21

On to step 4:
When dividing 34 by 21, we get 1 with a remainder of 13.
The next digit of our result is 1. 
Result so far: 381.0
Subtract 21 from 34 to get 13.
Take the next digit (2) from the dividend and append it to 13, then repeat: 132 / 21

Let's proceed to step 5:
If we divide 132 by 21, we get 6 and a remainder of 6.
Write down 6 as next digit of the result. 
Result so far: 3816.0
Subtract 126 from 132 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.

On to step 6:
The number 21 fits into 60 2 times, leaving a remainder of 18.
Put 2 as the next digit of the answer. 
Result so far: 3816.2
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.

Going ahead to step 7:
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: 3816.28
Subtract 168 from 180 to get 12.
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 8:
If we divide 120 by 21, we get 5 and a remainder of 15.
Write down 5 as next digit of the result. 
Result so far: 3816.285
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.

Step 9:
If we divide 150 by 21, we get 7 and a remainder of 3.
Use 7 as the next digit of our solution. 
Result so far: 3816.2857
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 10:
21 goes into 30 1 times with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 3816.28571
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.

Going ahead to step 11:
21 can be fit into 90 4 times, resulting in a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 3816.285714
Deduct 84 from 90 and we're left with 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 12:
21 can be fit into 60 2 times, resulting in a remainder of 18.
The next digit of our result is 2. 
Result so far: 3816.2857142
The remainder is 18 after subtracting 42 from 60.
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 13:
21 can be fit into 180 8 times, resulting in a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 3816.28571428
Deduct 168 from 180 and we're left with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Our division results in 3816.28571428 with a remaining 1.2e-08.