We look at the division of 39373790 by 21 
Let's see how many times 21 fits into 39373790.

Step 1:
When dividing 3 by 21, we get 0 with a remainder of 3.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Deduct 0 from 3 and we're left with 3.
Include the next digit (9) from the dividend after 3, then repeat: 39 / 21

Advancing to step 2:
21 can be fit into 39 1 times, resulting in a remainder of 18.
Use 1 as the next digit of our solution. 
Result so far: 1.0
The remainder is 18 after subtracting 21 from 39.
Bring next digit (3) of the dividend behind the 18 and repeat the process: 183 / 21

Advancing to step 3:
When dividing 183 by 21, we get 8 with a remainder of 15.
Write down 8 as next digit of the result. 
Result so far: 18.0
Subtract 168 from 183 to get 15.
Bring next digit (7) of the dividend behind the 15 and repeat the process: 157 / 21

Let's proceed to step 4:
The number 21 fits into 157 7 times, leaving a remainder of 10.
Record the quotient 7 as the next digit in the result. 
Result so far: 187.0
The remainder is 10 after subtracting 147 from 157.
Bring next digit (3) of the dividend behind the 10 and repeat the process: 103 / 21

Going ahead to step 5:
21 can be fit into 103 4 times, resulting in a remainder of 19.
Write down 4 as next digit of the result. 
Result so far: 1874.0
The remainder is 19 after subtracting 84 from 103.
Append the next digit (7) from the dividend to 19 and continue with: 197 / 21

Going ahead to step 6:
When dividing 197 by 21, we get 9 with a remainder of 8.
Use 9 as the next digit of our solution. 
Result so far: 18749.0
The remainder is 8 after subtracting 189 from 197.
Take the next digit (9) from the dividend and append it to 8, then repeat: 89 / 21

On to step 7:
89 divided by 21 is 4 with a remainder of 5.
The next digit of our result is 4. 
Result so far: 187494.0
Subtract 84 from 89 to get 5.
Include the next digit (0) from the dividend after 5, then repeat: 50 / 21

Advancing to step 8:
21 can be fit into 50 2 times, resulting in a remainder of 8.
Use 2 as the next digit of our solution. 
Result so far: 1874942.0
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.

Moving on to step 9:
When dividing 80 by 21, we get 3 with a remainder of 17.
Record the quotient 3 as the next digit in the result. 
Result so far: 1874942.3
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.

On to step 10:
170 divided by 21 is 8 with a remainder of 2.
Put 8 as the next digit of the answer. 
Result so far: 1874942.38
The remainder is 2 after subtracting 168 from 170.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Going ahead to step 11:
20 divided by 21 is 0 with a remainder of 20.
The next digit of our result is 0. 
Result so far: 1874942.38
If we take 0 away from 20, we end up with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Step 12:
The number 21 fits into 200 9 times, leaving a remainder of 11.
Record the quotient 9 as the next digit in the result. 
Result so far: 1874942.3809
Deduct 189 from 200 and we're left 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.

Moving on to step 13:
If we divide 110 by 21, we get 5 and a remainder of 5.
The next digit of our result is 5. 
Result so far: 1874942.38095
Subtract 105 from 110 to 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.

On to step 14:
21 can be fit into 50 2 times, resulting in a remainder of 8.
Put 2 as the next digit of the answer. 
Result so far: 1874942.380952
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.

Advancing to step 15:
When dividing 80 by 21, we get 3 with a remainder of 17.
Use 3 as the next digit of our solution. 
Result so far: 1874942.3809523
If we subtract 63 from 80, we get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

On to step 16:
21 can be fit into 170 8 times, resulting in a remainder of 2.
Put 8 as the next digit of the answer. 
Result so far: 1874942.38095238
Deduct 168 from 170 and we're left with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

The final outcome is 1874942.38095238, with a leftover of 2e-09.