863999 ÷ 15 
The aim is to understand the frequency of 15 in 863999.

Let's proceed to step 1:
The number 15 fits into 8 0 times, leaving a remainder of 8.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtracting 0 from 8 leaves us with 8.
Bring next digit (6) of the dividend behind the 8 and repeat the process: 86 / 15

On to step 2:
15 goes into 86 5 times with a remainder of 11.
The number 5 becomes the next digit in our result. 
Result so far: 5.0
The remainder is 11 after subtracting 75 from 86.
Include the next digit (3) from the dividend after 11, then repeat: 113 / 15

Going ahead to step 3:
15 can be fit into 113 7 times, resulting in a remainder of 8.
Write down 7 as next digit of the result. 
Result so far: 57.0
If we subtract 105 from 113, we get 8.
Fetch the next digit (9) from the dividend, attach it to 8 and continue: 89 / 15

Let's proceed to step 4:
15 goes into 89 5 times with a remainder of 14.
Write down 5 as next digit of the result. 
Result so far: 575.0
Deduct 75 from 89 and we're left with 14.
Grab the next digit (9) from the dividend, add it to 14, then carry on: 149 / 15

On to step 5:
If we divide 149 by 15, we get 9 and a remainder of 14.
The number 9 becomes the next digit in our result. 
Result so far: 5759.0
If we take 135 away from 149, we end up with 14.
Take the next digit (9) from the dividend and append it to 14, then repeat: 149 / 15

Step 6:
If we divide 149 by 15, we get 9 and a remainder of 14.
Record the quotient 9 as the next digit in the result. 
Result so far: 57599.0
Subtract 135 from 149 to get 14.
Since there are no more digits in the dividend, we add a zero to the remainder making it 140, and continue the process.

Let's proceed to step 7:
The number 15 fits into 140 9 times, leaving a remainder of 5.
Record the quotient 9 as the next digit in the result. 
Result so far: 57599.9
Deduct 135 from 140 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.

Let's proceed to step 8:
15 can be fit into 50 3 times, resulting in a remainder of 5.
The next digit of our result is 3. 
Result so far: 57599.93
Deduct 45 from 50 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.

Moving on to step 9:
15 can be fit into 50 3 times, resulting in a remainder of 5.
Record the quotient 3 as the next digit in the result. 
Result so far: 57599.933
Subtracting 45 from 50 leaves us 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.

The quotient of the division is 57599.933, and the remainder is 0.0005.