We look at the division of 843974 by 90 
The aim is to understand the frequency of 90 in 843974.

Moving on to step 1:
8 divided by 90 is 0 with a remainder of 8.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 8, we end up with 8.
Append the next digit (4) from the dividend to 8 and continue with: 84 / 90

Going ahead to step 2:
90 can be fit into 84 0 times, resulting in a remainder of 84.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 84, we end up with 84.
Fetch the next digit (3) from the dividend, attach it to 84 and continue: 843 / 90

Let's proceed to step 3:
When dividing 843 by 90, we get 9 with a remainder of 33.
Use 9 as the next digit of our solution. 
Result so far: 9.0
If we take 810 away from 843, we end up with 33.
Include the next digit (9) from the dividend after 33, then repeat: 339 / 90

On to step 4:
90 goes into 339 3 times with a remainder of 69.
Put 3 as the next digit of the answer. 
Result so far: 93.0
The remainder is 69 after subtracting 270 from 339.
Take the next digit (7) from the dividend and append it to 69, then repeat: 697 / 90

Advancing to step 5:
The number 90 fits into 697 7 times, leaving a remainder of 67.
The next digit of our result is 7. 
Result so far: 937.0
Subtracting 630 from 697 leaves us with 67.
Take the next digit (4) from the dividend and append it to 67, then repeat: 674 / 90

Going ahead to step 6:
When dividing 674 by 90, we get 7 with a remainder of 44.
The number 7 becomes the next digit in our result. 
Result so far: 9377.0
The remainder is 44 after subtracting 630 from 674.
Since there are no more digits in the dividend, we add a zero to the remainder making it 440, and continue the process.

Let's proceed to step 7:
When dividing 440 by 90, we get 4 with a remainder of 80.
The number 4 becomes the next digit in our result. 
Result so far: 9377.4
If we subtract 360 from 440, we get 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 800, and continue the process.

Going ahead to step 8:
When dividing 800 by 90, we get 8 with a remainder of 80.
Write down 8 as next digit of the result. 
Result so far: 9377.48
Subtracting 720 from 800 leaves us with 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 800, and continue the process.

Step 9:
The number 90 fits into 800 8 times, leaving a remainder of 80.
Put 8 as the next digit of the answer. 
Result so far: 9377.488
Subtract 720 from 800 to get 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 800, and continue the process.

After the division, we end up with 9377.488 and a remainder of 0.008.