We look at the division of 390742 by 90 
The aim is to understand the frequency of 90 in 390742.

Advancing to step 1:
When dividing 3 by 90, we get 0 with a remainder of 3.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtract 0 from 3 to get 3.
Bring next digit (9) of the dividend behind the 3 and repeat the process: 39 / 90

On to step 2:
If we divide 39 by 90, we get 0 and a remainder of 39.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we subtract 0 from 39, we get 39.
Grab the next digit (0) from the dividend, add it to 39, then carry on: 390 / 90

On to step 3:
When dividing 390 by 90, we get 4 with a remainder of 30.
Write down 4 as next digit of the result. 
Result so far: 4.0
If we subtract 360 from 390, we get 30.
Take the next digit (7) from the dividend and append it to 30, then repeat: 307 / 90

Going ahead to step 4:
90 can be fit into 307 3 times, resulting in a remainder of 37.
The next digit of our result is 3. 
Result so far: 43.0
Subtracting 270 from 307 leaves us with 37.
Append the next digit (4) from the dividend to 37 and continue with: 374 / 90

Moving on to step 5:
374 divided by 90 is 4 with a remainder of 14.
Record the quotient 4 as the next digit in the result. 
Result so far: 434.0
The remainder is 14 after subtracting 360 from 374.
Take the next digit (2) from the dividend and append it to 14, then repeat: 142 / 90

Advancing to step 6:
The number 90 fits into 142 1 times, leaving a remainder of 52.
The number 1 becomes the next digit in our result. 
Result so far: 4341.0
If we take 90 away from 142, we end up with 52.
Since there are no more digits in the dividend, we add a zero to the remainder making it 520, and continue the process.

Moving on to step 7:
If we divide 520 by 90, we get 5 and a remainder of 70.
The next digit of our result is 5. 
Result so far: 4341.5
If we take 450 away from 520, we end up with 70.
Since there are no more digits in the dividend, we add a zero to the remainder making it 700, and continue the process.

Going ahead to step 8:
When dividing 700 by 90, we get 7 with a remainder of 70.
Put 7 as the next digit of the answer. 
Result so far: 4341.57
Subtracting 630 from 700 leaves us with 70.
Since there are no more digits in the dividend, we add a zero to the remainder making it 700, and continue the process.

On to step 9:
90 can be fit into 700 7 times, resulting in a remainder of 70.
Record the quotient 7 as the next digit in the result. 
Result so far: 4341.577
Subtract 630 from 700 to get 70.
Since there are no more digits in the dividend, we add a zero to the remainder making it 700, and continue the process.

Our division results in 4341.577 with a remaining 0.007.