21258638 ÷ 15 
We want to divide 21258638 by 15.

Advancing to step 1:
The number 15 fits into 2 0 times, leaving a remainder of 2.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtracting 0 from 2 leaves us with 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 15

Going ahead to step 2:
15 goes into 21 1 times with a remainder of 6.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
The remainder is 6 after subtracting 15 from 21.
Bring next digit (2) of the dividend behind the 6 and repeat the process: 62 / 15

Let's proceed to step 3:
If we divide 62 by 15, we get 4 and a remainder of 2.
Record the quotient 4 as the next digit in the result. 
Result so far: 14.0
Deduct 60 from 62 and we're left with 2.
Fetch the next digit (5) from the dividend, attach it to 2 and continue: 25 / 15

On to step 4:
The number 15 fits into 25 1 times, leaving a remainder of 10.
Put 1 as the next digit of the answer. 
Result so far: 141.0
If we take 15 away from 25, we end up with 10.
Append the next digit (8) from the dividend to 10 and continue with: 108 / 15

Step 5:
When dividing 108 by 15, we get 7 with a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 1417.0
Subtracting 105 from 108 leaves us with 3.
Fetch the next digit (6) from the dividend, attach it to 3 and continue: 36 / 15

On to step 6:
The number 15 fits into 36 2 times, leaving a remainder of 6.
The number 2 becomes the next digit in our result. 
Result so far: 14172.0
If we take 30 away from 36, we end up with 6.
Fetch the next digit (3) from the dividend, attach it to 6 and continue: 63 / 15

Moving on to step 7:
15 can be fit into 63 4 times, resulting in a remainder of 3.
The next digit of our result is 4. 
Result so far: 141724.0
If we subtract 60 from 63, we get 3.
Include the next digit (8) from the dividend after 3, then repeat: 38 / 15

Going ahead to step 8:
If we divide 38 by 15, we get 2 and a remainder of 8.
Put 2 as the next digit of the answer. 
Result so far: 1417242.0
Subtract 30 from 38 to 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.

Let's proceed to step 9:
The number 15 fits into 80 5 times, leaving a remainder of 5.
The next digit of our result is 5. 
Result so far: 1417242.5
Deduct 75 from 80 and we're left 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 10:
If we divide 50 by 15, we get 3 and a remainder of 5.
The number 3 becomes the next digit in our result. 
Result so far: 1417242.53
Subtract 45 from 50 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.

Advancing to step 11:
15 can be fit into 50 3 times, resulting in a remainder of 5.
The number 3 becomes the next digit in our result. 
Result so far: 1417242.533
Subtract 45 from 50 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.

The quotient of the division is 1417242.533, and the remainder is 0.0005.