We look at the division of 815987 by 77 
The aim is to understand the frequency of 77 in 815987.

Going ahead to step 1:
77 can be fit into 8 0 times, resulting in a remainder of 8.
The next digit of our result is 0. 
Result so far: 0.0
If we subtract 0 from 8, we get 8.
Bring next digit (1) of the dividend behind the 8 and repeat the process: 81 / 77

Going ahead to step 2:
The number 77 fits into 81 1 times, leaving a remainder of 4.
The next digit of our result is 1. 
Result so far: 1.0
Subtracting 77 from 81 leaves us with 4.
Fetch the next digit (5) from the dividend, attach it to 4 and continue: 45 / 77

Let's proceed to step 3:
The number 77 fits into 45 0 times, leaving a remainder of 45.
Write down 0 as next digit of the result. 
Result so far: 10.0
The remainder is 45 after subtracting 0 from 45.
Take the next digit (9) from the dividend and append it to 45, then repeat: 459 / 77

Advancing to step 4:
77 goes into 459 5 times with a remainder of 74.
Write down 5 as next digit of the result. 
Result so far: 105.0
Deduct 385 from 459 and we're left with 74.
Bring next digit (8) of the dividend behind the 74 and repeat the process: 748 / 77

Going ahead to step 5:
If we divide 748 by 77, we get 9 and a remainder of 55.
Write down 9 as next digit of the result. 
Result so far: 1059.0
Subtracting 693 from 748 leaves us with 55.
Grab the next digit (7) from the dividend, add it to 55, then carry on: 557 / 77

On to step 6:
557 divided by 77 is 7 with a remainder of 18.
Write down 7 as next digit of the result. 
Result so far: 10597.0
Subtracting 539 from 557 leaves us with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Moving on to step 7:
77 can be fit into 180 2 times, resulting in a remainder of 26.
Write down 2 as next digit of the result. 
Result so far: 10597.2
Subtract 154 from 180 to get 26.
Since there are no more digits in the dividend, we add a zero to the remainder making it 260, and continue the process.

Advancing to step 8:
77 goes into 260 3 times with a remainder of 29.
The next digit of our result is 3. 
Result so far: 10597.23
Subtract 231 from 260 to get 29.
Since there are no more digits in the dividend, we add a zero to the remainder making it 290, and continue the process.

Advancing to step 9:
77 can be fit into 290 3 times, resulting in a remainder of 59.
Put 3 as the next digit of the answer. 
Result so far: 10597.233
If we subtract 231 from 290, we get 59.
Since there are no more digits in the dividend, we add a zero to the remainder making it 590, and continue the process.

The final outcome is 10597.233, with a leftover of 0.0059.