39664639 ÷ 21 
We want to figure out the number of times 39664639 can be divided by 21.

Advancing to step 1:
If we divide 3 by 21, we get 0 and a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we take 0 away from 3, we end up with 3.
Fetch the next digit (9) from the dividend, attach it to 3 and continue: 39 / 21

Moving on to step 2:
21 goes into 39 1 times with a remainder of 18.
Use 1 as the next digit of our solution. 
Result so far: 1.0
If we subtract 21 from 39, we get 18.
Bring next digit (6) of the dividend behind the 18 and repeat the process: 186 / 21

Step 3:
If we divide 186 by 21, we get 8 and a remainder of 18.
Write down 8 as next digit of the result. 
Result so far: 18.0
Deduct 168 from 186 and we're left with 18.
Take the next digit (6) from the dividend and append it to 18, then repeat: 186 / 21

On to step 4:
186 divided by 21 is 8 with a remainder of 18.
Use 8 as the next digit of our solution. 
Result so far: 188.0
If we take 168 away from 186, we end up with 18.
Bring next digit (4) of the dividend behind the 18 and repeat the process: 184 / 21

Let's proceed to step 5:
21 can be fit into 184 8 times, resulting in a remainder of 16.
Use 8 as the next digit of our solution. 
Result so far: 1888.0
If we subtract 168 from 184, we get 16.
Include the next digit (6) from the dividend after 16, then repeat: 166 / 21

Step 6:
21 goes into 166 7 times with a remainder of 19.
Use 7 as the next digit of our solution. 
Result so far: 18887.0
The remainder is 19 after subtracting 147 from 166.
Append the next digit (3) from the dividend to 19 and continue with: 193 / 21

On to step 7:
The number 21 fits into 193 9 times, leaving a remainder of 4.
The next digit of our result is 9. 
Result so far: 188879.0
If we subtract 189 from 193, we get 4.
Fetch the next digit (9) from the dividend, attach it to 4 and continue: 49 / 21

Advancing to step 8:
49 divided by 21 is 2 with a remainder of 7.
The next digit of our result is 2. 
Result so far: 1888792.0
Subtract 42 from 49 to get 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Going ahead to step 9:
If we divide 70 by 21, we get 3 and a remainder of 7.
The number 3 becomes the next digit in our result. 
Result so far: 1888792.3
Deduct 63 from 70 and we're left with 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Step 10:
The number 21 fits into 70 3 times, leaving a remainder of 7.
Use 3 as the next digit of our solution. 
Result so far: 1888792.33
Deduct 63 from 70 and we're left with 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

The quotient of the division is 1888792.33, and the remainder is 0.007.