We look at the division of 661673 by 90 
The aim is to understand the frequency of 90 in 661673.

Going ahead to step 1:
The number 90 fits into 6 0 times, leaving 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.
Append the next digit (6) from the dividend to 6 and continue with: 66 / 90

Moving on to step 2:
When dividing 66 by 90, we get 0 with a remainder of 66.
The next digit of our result is 0. 
Result so far: 0.0
Subtracting 0 from 66 leaves us with 66.
Include the next digit (1) from the dividend after 66, then repeat: 661 / 90

Step 3:
The number 90 fits into 661 7 times, leaving a remainder of 31.
Record the quotient 7 as the next digit in the result. 
Result so far: 7.0
If we take 630 away from 661, we end up with 31.
Fetch the next digit (6) from the dividend, attach it to 31 and continue: 316 / 90

Step 4:
90 goes into 316 3 times with a remainder of 46.
Record the quotient 3 as the next digit in the result. 
Result so far: 73.0
If we take 270 away from 316, we end up with 46.
Fetch the next digit (7) from the dividend, attach it to 46 and continue: 467 / 90

Let's proceed to step 5:
467 divided by 90 is 5 with a remainder of 17.
The next digit of our result is 5. 
Result so far: 735.0
If we subtract 450 from 467, we get 17.
Include the next digit (3) from the dividend after 17, then repeat: 173 / 90

Advancing to step 6:
173 divided by 90 is 1 with a remainder of 83.
Put 1 as the next digit of the answer. 
Result so far: 7351.0
If we subtract 90 from 173, we get 83.
Since there are no more digits in the dividend, we add a zero to the remainder making it 830, and continue the process.

On to step 7:
90 goes into 830 9 times with a remainder of 20.
Write down 9 as next digit of the result. 
Result so far: 7351.9
If we subtract 810 from 830, we 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.

On to step 8:
90 goes into 200 2 times with a remainder of 20.
The number 2 becomes the next digit in our result. 
Result so far: 7351.92
The remainder is 20 after subtracting 180 from 200.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Let's proceed to step 9:
When dividing 200 by 90, we get 2 with a remainder of 20.
Record the quotient 2 as the next digit in the result. 
Result so far: 7351.922
The remainder is 20 after subtracting 180 from 200.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

In conclusion, the division gives 7351.922 with a balance of 0.002.