987984 ÷ 13 
The aim is to understand the frequency of 13 in 987984.

Let's proceed to step 1:
13 can be fit into 9 0 times, resulting in a remainder of 9.
Write down 0 as next digit of the result. 
Result so far: 0.0
Deduct 0 from 9 and we're left with 9.
Include the next digit (8) from the dividend after 9, then repeat: 98 / 13

Let's proceed to step 2:
If we divide 98 by 13, we get 7 and a remainder of 7.
Record the quotient 7 as the next digit in the result. 
Result so far: 7.0
Subtracting 91 from 98 leaves us with 7.
Take the next digit (7) from the dividend and append it to 7, then repeat: 77 / 13

Let's proceed to step 3:
13 goes into 77 5 times with a remainder of 12.
Write down 5 as next digit of the result. 
Result so far: 75.0
Deduct 65 from 77 and we're left with 12.
Bring next digit (9) of the dividend behind the 12 and repeat the process: 129 / 13

Let's proceed to step 4:
13 can be fit into 129 9 times, resulting in a remainder of 12.
Use 9 as the next digit of our solution. 
Result so far: 759.0
Deduct 117 from 129 and we're left with 12.
Take the next digit (8) from the dividend and append it to 12, then repeat: 128 / 13

Advancing to step 5:
13 goes into 128 9 times with a remainder of 11.
Write down 9 as next digit of the result. 
Result so far: 7599.0
Subtract 117 from 128 to get 11.
Fetch the next digit (4) from the dividend, attach it to 11 and continue: 114 / 13

Let's proceed to step 6:
If we divide 114 by 13, we get 8 and a remainder of 10.
The number 8 becomes the next digit in our result. 
Result so far: 75998.0
The remainder is 10 after subtracting 104 from 114.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Let's proceed to step 7:
If we divide 100 by 13, we get 7 and a remainder of 9.
The number 7 becomes the next digit in our result. 
Result so far: 75998.7
Subtracting 91 from 100 leaves us with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Moving on to step 8:
90 divided by 13 is 6 with a remainder of 12.
Put 6 as the next digit of the answer. 
Result so far: 75998.76
If we take 78 away from 90, we end up 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.

Going ahead to step 9:
The number 13 fits into 120 9 times, leaving a remainder of 3.
The number 9 becomes the next digit in our result. 
Result so far: 75998.769
If we take 117 away from 120, we end up with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

On to step 10:
13 goes into 30 2 times with a remainder of 4.
Write down 2 as next digit of the result. 
Result so far: 75998.7692
The remainder is 4 after subtracting 26 from 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Step 11:
When dividing 40 by 13, we get 3 with a remainder of 1.
Write down 3 as next digit of the result. 
Result so far: 75998.76923
If we take 39 away from 40, we end up with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Advancing to step 12:
The number 13 fits into 10 0 times, leaving a remainder of 10.
The number 0 becomes the next digit in our result. 
Result so far: 75998.76923
The remainder is 10 after subtracting 0 from 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Moving on to step 13:
100 divided by 13 is 7 with a remainder of 9.
The number 7 becomes the next digit in our result. 
Result so far: 75998.7692307
The remainder is 9 after subtracting 91 from 100.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Going ahead to step 14:
13 can be fit into 90 6 times, resulting in a remainder of 12.
The next digit of our result is 6. 
Result so far: 75998.76923076
The remainder is 12 after subtracting 78 from 90.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

The final outcome is 75998.76923076, with a leftover of 1.2e-08.