We look at the division of 17980135 by 28 
The aim is to understand the frequency of 28 in 17980135.

On to step 1:
1 divided by 28 is 0 with a remainder of 1.
Use 0 as the next digit of our solution. 
Result so far: 0.0
The remainder is 1 after subtracting 0 from 1.
Grab the next digit (7) from the dividend, add it to 1, then carry on: 17 / 28

On to step 2:
If we divide 17 by 28, we get 0 and a remainder of 17.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Deduct 0 from 17 and we're left with 17.
Include the next digit (9) from the dividend after 17, then repeat: 179 / 28

Step 3:
When dividing 179 by 28, we get 6 with a remainder of 11.
The next digit of our result is 6. 
Result so far: 6.0
If we subtract 168 from 179, we get 11.
Take the next digit (8) from the dividend and append it to 11, then repeat: 118 / 28

On to step 4:
If we divide 118 by 28, we get 4 and a remainder of 6.
Use 4 as the next digit of our solution. 
Result so far: 64.0
Deduct 112 from 118 and we're left with 6.
Grab the next digit (0) from the dividend, add it to 6, then carry on: 60 / 28

Step 5:
If we divide 60 by 28, we get 2 and a remainder of 4.
The next digit of our result is 2. 
Result so far: 642.0
The remainder is 4 after subtracting 56 from 60.
Bring next digit (1) of the dividend behind the 4 and repeat the process: 41 / 28

On to step 6:
When dividing 41 by 28, we get 1 with a remainder of 13.
Record the quotient 1 as the next digit in the result. 
Result so far: 6421.0
Subtract 28 from 41 to get 13.
Append the next digit (3) from the dividend to 13 and continue with: 133 / 28

Let's proceed to step 7:
When dividing 133 by 28, we get 4 with a remainder of 21.
Write down 4 as next digit of the result. 
Result so far: 64214.0
If we take 112 away from 133, we end up with 21.
Grab the next digit (5) from the dividend, add it to 21, then carry on: 215 / 28

Moving on to step 8:
When dividing 215 by 28, we get 7 with a remainder of 19.
The next digit of our result is 7. 
Result so far: 642147.0
If we subtract 196 from 215, we get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Moving on to step 9:
28 goes into 190 6 times with a remainder of 22.
The next digit of our result is 6. 
Result so far: 642147.6
If we subtract 168 from 190, we get 22.
Since there are no more digits in the dividend, we add a zero to the remainder making it 220, and continue the process.

Moving on to step 10:
220 divided by 28 is 7 with a remainder of 24.
Write down 7 as next digit of the result. 
Result so far: 642147.67
If we take 196 away from 220, we end up with 24.
Since there are no more digits in the dividend, we add a zero to the remainder making it 240, and continue the process.

Step 11:
The number 28 fits into 240 8 times, leaving a remainder of 16.
Use 8 as the next digit of our solution. 
Result so far: 642147.678
If we take 224 away from 240, we end up with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Advancing to step 12:
When dividing 160 by 28, we get 5 with a remainder of 20.
Put 5 as the next digit of the answer. 
Result so far: 642147.6785
Subtract 140 from 160 to get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Going ahead to step 13:
28 can be fit into 200 7 times, resulting in a remainder of 4.
Put 7 as the next digit of the answer. 
Result so far: 642147.67857
If we subtract 196 from 200, 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.

Moving on to step 14:
If we divide 40 by 28, we get 1 and a remainder of 12.
Put 1 as the next digit of the answer. 
Result so far: 642147.678571
Deduct 28 from 40 and we're left with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Step 15:
28 can be fit into 120 4 times, resulting in a remainder of 8.
Put 4 as the next digit of the answer. 
Result so far: 642147.6785714
Subtract 112 from 120 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.

On to step 16:
28 can be fit into 80 2 times, resulting in a remainder of 24.
The next digit of our result is 2. 
Result so far: 642147.67857142
Deduct 56 from 80 and we're left with 24.
Since there are no more digits in the dividend, we add a zero to the remainder making it 240, and continue the process.

The final result is 642147.67857142 with a remainder of 2.4e-08.