We look at the division of 644728 by 18 
The aim is to understand the frequency of 18 in 644728.

Moving on to step 1:
When dividing 6 by 18, we get 0 with a remainder of 6.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtracting 0 from 6 leaves us with 6.
Fetch the next digit (4) from the dividend, attach it to 6 and continue: 64 / 18

Moving on to step 2:
The number 18 fits into 64 3 times, leaving a remainder of 10.
Record the quotient 3 as the next digit in the result. 
Result so far: 3.0
Subtracting 54 from 64 leaves us with 10.
Fetch the next digit (4) from the dividend, attach it to 10 and continue: 104 / 18

Let's proceed to step 3:
If we divide 104 by 18, we get 5 and a remainder of 14.
Write down 5 as next digit of the result. 
Result so far: 35.0
Subtract 90 from 104 to get 14.
Bring next digit (7) of the dividend behind the 14 and repeat the process: 147 / 18

Advancing to step 4:
The number 18 fits into 147 8 times, leaving a remainder of 3.
Write down 8 as next digit of the result. 
Result so far: 358.0
Subtract 144 from 147 to get 3.
Grab the next digit (2) from the dividend, add it to 3, then carry on: 32 / 18

Let's proceed to step 5:
The number 18 fits into 32 1 times, leaving a remainder of 14.
The number 1 becomes the next digit in our result. 
Result so far: 3581.0
Deduct 18 from 32 and we're left with 14.
Take the next digit (8) from the dividend and append it to 14, then repeat: 148 / 18

Let's proceed to step 6:
148 divided by 18 is 8 with a remainder of 4.
Write down 8 as next digit of the result. 
Result so far: 35818.0
If we take 144 away from 148, we end up with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Let's proceed to step 7:
The number 18 fits into 40 2 times, leaving a remainder of 4.
Put 2 as the next digit of the answer. 
Result so far: 35818.2
If we subtract 36 from 40, we get 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Going ahead to step 8:
18 goes into 40 2 times with a remainder of 4.
Put 2 as the next digit of the answer. 
Result so far: 35818.22
Deduct 36 from 40 and we're left with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

The final outcome is 35818.22, with a leftover of 0.004.