643187 divided by 18 
The aim is to understand the frequency of 18 in 643187.

Moving on to step 1:
18 goes into 6 0 times with a remainder of 6.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 6 to get 6.
Fetch the next digit (4) from the dividend, attach it to 6 and continue: 64 / 18

Step 2:
If we divide 64 by 18, we get 3 and a remainder of 10.
Put 3 as the next digit of the answer. 
Result so far: 3.0
Deduct 54 from 64 and we're left with 10.
Append the next digit (3) from the dividend to 10 and continue with: 103 / 18

Step 3:
18 can be fit into 103 5 times, resulting in a remainder of 13.
The number 5 becomes the next digit in our result. 
Result so far: 35.0
Subtracting 90 from 103 leaves us with 13.
Append the next digit (1) from the dividend to 13 and continue with: 131 / 18

Let's proceed to step 4:
When dividing 131 by 18, we get 7 with a remainder of 5.
The next digit of our result is 7. 
Result so far: 357.0
Subtract 126 from 131 to get 5.
Fetch the next digit (8) from the dividend, attach it to 5 and continue: 58 / 18

Advancing to step 5:
18 can be fit into 58 3 times, resulting in a remainder of 4.
The next digit of our result is 3. 
Result so far: 3573.0
Subtracting 54 from 58 leaves us with 4.
Take the next digit (7) from the dividend and append it to 4, then repeat: 47 / 18

Going ahead to step 6:
If we divide 47 by 18, we get 2 and a remainder of 11.
Put 2 as the next digit of the answer. 
Result so far: 35732.0
Subtracting 36 from 47 leaves us 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.

Going ahead to step 7:
If we divide 110 by 18, we get 6 and a remainder of 2.
Record the quotient 6 as the next digit in the result. 
Result so far: 35732.6
Subtract 108 from 110 to get 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Moving on to step 8:
When dividing 20 by 18, we get 1 with a remainder of 2.
Put 1 as the next digit of the answer. 
Result so far: 35732.61
If we subtract 18 from 20, we get 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

On to step 9:
18 goes into 20 1 times with a remainder of 2.
Write down 1 as next digit of the result. 
Result so far: 35732.611
Subtracting 18 from 20 leaves us 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 quotient of the division is 35732.611, and the remainder is 0.0002.