145561 ÷ 90 
The aim is to understand the frequency of 90 in 145561.

On to step 1:
90 goes into 1 0 times with a remainder of 1.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Deduct 0 from 1 and we're left with 1.
Bring next digit (4) of the dividend behind the 1 and repeat the process: 14 / 90

Let's proceed to step 2:
90 can be fit into 14 0 times, resulting in a remainder of 14.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtracting 0 from 14 leaves us with 14.
Grab the next digit (5) from the dividend, add it to 14, then carry on: 145 / 90

Moving on to step 3:
The number 90 fits into 145 1 times, leaving a remainder of 55.
Use 1 as the next digit of our solution. 
Result so far: 1.0
Deduct 90 from 145 and we're left with 55.
Take the next digit (5) from the dividend and append it to 55, then repeat: 555 / 90

Step 4:
90 goes into 555 6 times with a remainder of 15.
Record the quotient 6 as the next digit in the result. 
Result so far: 16.0
The remainder is 15 after subtracting 540 from 555.
Grab the next digit (6) from the dividend, add it to 15, then carry on: 156 / 90

Advancing to step 5:
90 can be fit into 156 1 times, resulting in a remainder of 66.
Write down 1 as next digit of the result. 
Result so far: 161.0
Subtracting 90 from 156 leaves us with 66.
Grab the next digit (1) from the dividend, add it to 66, then carry on: 661 / 90

Advancing to step 6:
When dividing 661 by 90, we get 7 with a remainder of 31.
The next digit of our result is 7. 
Result so far: 1617.0
Deduct 630 from 661 and we're left with 31.
Since there are no more digits in the dividend, we add a zero to the remainder making it 310, and continue the process.

Let's proceed to step 7:
90 can be fit into 310 3 times, resulting in a remainder of 40.
Use 3 as the next digit of our solution. 
Result so far: 1617.3
If we subtract 270 from 310, we get 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 400, and continue the process.

Going ahead to step 8:
When dividing 400 by 90, we get 4 with a remainder of 40.
The next digit of our result is 4. 
Result so far: 1617.34
Subtract 360 from 400 to get 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 400, and continue the process.

Advancing to step 9:
The number 90 fits into 400 4 times, leaving a remainder of 40.
Put 4 as the next digit of the answer. 
Result so far: 1617.344
Deduct 360 from 400 and we're left with 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 400, and continue the process.

The final result is 1617.344 with a remainder of 0.004.