We're dividing 351972 by 21 
We're looking to find how many times 21 goes into 351972.

Step 1:
The number 21 fits into 3 0 times, leaving a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
The remainder is 3 after subtracting 0 from 3.
Append the next digit (5) from the dividend to 3 and continue with: 35 / 21

Let's proceed to step 2:
If we divide 35 by 21, we get 1 and a remainder of 14.
Write down 1 as next digit of the result. 
Result so far: 1.0
If we subtract 21 from 35, we get 14.
Take the next digit (1) from the dividend and append it to 14, then repeat: 141 / 21

Let's proceed to step 3:
The number 21 fits into 141 6 times, leaving a remainder of 15.
The next digit of our result is 6. 
Result so far: 16.0
Deduct 126 from 141 and we're left with 15.
Fetch the next digit (9) from the dividend, attach it to 15 and continue: 159 / 21

Advancing to step 4:
21 can be fit into 159 7 times, resulting in a remainder of 12.
The next digit of our result is 7. 
Result so far: 167.0
If we subtract 147 from 159, we get 12.
Fetch the next digit (7) from the dividend, attach it to 12 and continue: 127 / 21

Let's proceed to step 5:
21 goes into 127 6 times with a remainder of 1.
The next digit of our result is 6. 
Result so far: 1676.0
The remainder is 1 after subtracting 126 from 127.
Take the next digit (2) from the dividend and append it to 1, then repeat: 12 / 21

Let's proceed to step 6:
The number 21 fits into 12 0 times, leaving a remainder of 12.
Put 0 as the next digit of the answer. 
Result so far: 16760.0
If we take 0 away from 12, we end up 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.

On to step 7:
120 divided by 21 is 5 with a remainder of 15.
Use 5 as the next digit of our solution. 
Result so far: 16760.5
If we subtract 105 from 120, we 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 8:
21 goes into 150 7 times with a remainder of 3.
The number 7 becomes the next digit in our result. 
Result so far: 16760.57
Subtract 147 from 150 to 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.

Moving on to step 9:
The number 21 fits into 30 1 times, leaving a remainder of 9.
The next digit of our result is 1. 
Result so far: 16760.571
Subtracting 21 from 30 leaves us with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Advancing to step 10:
If we divide 90 by 21, we get 4 and a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 16760.5714
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.

Let's proceed to step 11:
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: 16760.57142
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 12:
21 goes into 180 8 times with a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 16760.571428
If we take 168 away from 180, we end up 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.

Let's proceed to step 13:
120 divided by 21 is 5 with a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 16760.5714285
Subtracting 105 from 120 leaves us with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Let's proceed to step 14:
The number 21 fits into 150 7 times, leaving a remainder of 3.
The number 7 becomes the next digit in our result. 
Result so far: 16760.57142857
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.

The quotient of the division is 16760.57142857, and the remainder is 3e-09.