163378 ÷ 21 
The aim is to understand the frequency of 21 in 163378.

On to step 1:
21 can be fit into 1 0 times, resulting in a remainder of 1.
Use 0 as the next digit of our solution. 
Result so far: 0.0
The remainder is 1 after subtracting 0 from 1.
Append the next digit (6) from the dividend to 1 and continue with: 16 / 21

On to step 2:
21 goes into 16 0 times with a remainder of 16.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Deduct 0 from 16 and we're left with 16.
Append the next digit (3) from the dividend to 16 and continue with: 163 / 21

Advancing to step 3:
The number 21 fits into 163 7 times, leaving a remainder of 16.
Record the quotient 7 as the next digit in the result. 
Result so far: 7.0
The remainder is 16 after subtracting 147 from 163.
Grab the next digit (3) from the dividend, add it to 16, then carry on: 163 / 21

Step 4:
The number 21 fits into 163 7 times, leaving a remainder of 16.
Put 7 as the next digit of the answer. 
Result so far: 77.0
Subtract 147 from 163 to get 16.
Grab the next digit (7) from the dividend, add it to 16, then carry on: 167 / 21

Advancing to step 5:
21 can be fit into 167 7 times, resulting in a remainder of 20.
Put 7 as the next digit of the answer. 
Result so far: 777.0
Subtracting 147 from 167 leaves us with 20.
Fetch the next digit (8) from the dividend, attach it to 20 and continue: 208 / 21

Advancing to step 6:
When dividing 208 by 21, we get 9 with a remainder of 19.
The number 9 becomes the next digit in our result. 
Result so far: 7779.0
Subtracting 189 from 208 leaves us with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Advancing to step 7:
The number 21 fits into 190 9 times, leaving a remainder of 1.
Use 9 as the next digit of our solution. 
Result so far: 7779.9
If we take 189 away from 190, we end up with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Step 8:
21 goes into 10 0 times with a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 7779.9
Deduct 0 from 10 and we're left with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

On to step 9:
21 can be fit into 100 4 times, resulting in a remainder of 16.
Write down 4 as next digit of the result. 
Result so far: 7779.904
Deduct 84 from 100 and we're left with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Step 10:
When dividing 160 by 21, we get 7 with a remainder of 13.
The next digit of our result is 7. 
Result so far: 7779.9047
Deduct 147 from 160 and we're left with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Moving on to step 11:
21 goes into 130 6 times with a remainder of 4.
Record the quotient 6 as the next digit in the result. 
Result so far: 7779.90476
If we take 126 away from 130, we end up with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

On to step 12:
When dividing 40 by 21, we get 1 with a remainder of 19.
Use 1 as the next digit of our solution. 
Result so far: 7779.904761
Subtracting 21 from 40 leaves us with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Step 13:
The number 21 fits into 190 9 times, leaving a remainder of 1.
The next digit of our result is 9. 
Result so far: 7779.9047619
Deduct 189 from 190 and we're left with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Moving on to step 14:
When dividing 10 by 21, we get 0 with a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 7779.9047619
Subtracting 0 from 10 leaves us with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

The final outcome is 7779.9047619, with a leftover of 1e-08.