We look at the division of 390059 by 90 
The aim is to understand the frequency of 90 in 390059.

On to step 1:
3 divided by 90 is 0 with a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we take 0 away from 3, we end up with 3.
Bring next digit (9) of the dividend behind the 3 and repeat the process: 39 / 90

Going ahead to step 2:
If we divide 39 by 90, we get 0 and a remainder of 39.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtract 0 from 39 to get 39.
Include the next digit (0) from the dividend after 39, then repeat: 390 / 90

Let's proceed to step 3:
The number 90 fits into 390 4 times, leaving a remainder of 30.
Write down 4 as next digit of the result. 
Result so far: 4.0
Deduct 360 from 390 and we're left with 30.
Grab the next digit (0) from the dividend, add it to 30, then carry on: 300 / 90

On to step 4:
300 divided by 90 is 3 with a remainder of 30.
Record the quotient 3 as the next digit in the result. 
Result so far: 43.0
Subtract 270 from 300 to get 30.
Append the next digit (5) from the dividend to 30 and continue with: 305 / 90

Advancing to step 5:
The number 90 fits into 305 3 times, leaving a remainder of 35.
The next digit of our result is 3. 
Result so far: 433.0
If we take 270 away from 305, we end up with 35.
Bring next digit (9) of the dividend behind the 35 and repeat the process: 359 / 90

Moving on to step 6:
90 goes into 359 3 times with a remainder of 89.
The number 3 becomes the next digit in our result. 
Result so far: 4333.0
Subtract 270 from 359 to get 89.
Since there are no more digits in the dividend, we add a zero to the remainder making it 890, and continue the process.

Advancing to step 7:
90 can be fit into 890 9 times, resulting in a remainder of 80.
Record the quotient 9 as the next digit in the result. 
Result so far: 4333.9
The remainder is 80 after subtracting 810 from 890.
Since there are no more digits in the dividend, we add a zero to the remainder making it 800, and continue the process.

Step 8:
90 can be fit into 800 8 times, resulting in a remainder of 80.
Write down 8 as next digit of the result. 
Result so far: 4333.98
Deduct 720 from 800 and we're left 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.

On to step 9:
800 divided by 90 is 8 with a remainder of 80.
The number 8 becomes the next digit in our result. 
Result so far: 4333.988
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.

The final outcome is 4333.988, with a leftover of 0.008.