We look at the division of 861945 by 21 
We want to figure out the number of times 861945 can be divided by 21.

Moving on to step 1:
The number 21 fits into 8 0 times, leaving a remainder of 8.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Deduct 0 from 8 and we're left with 8.
Fetch the next digit (6) from the dividend, attach it to 8 and continue: 86 / 21

Moving on to step 2:
86 divided by 21 is 4 with a remainder of 2.
Record the quotient 4 as the next digit in the result. 
Result so far: 4.0
Deduct 84 from 86 and we're left with 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 21

Advancing to step 3:
21 divided by 21 is 1 with a remainder of 0.
Put 1 as the next digit of the answer. 
Result so far: 41.0
Subtract 21 from 21 to get 0.
Take the next digit (9) from the dividend and append it to 0, then repeat: 9 / 21

Let's proceed to step 4:
If we divide 9 by 21, we get 0 and a remainder of 9.
The number 0 becomes the next digit in our result. 
Result so far: 410.0
Subtracting 0 from 9 leaves us with 9.
Append the next digit (4) from the dividend to 9 and continue with: 94 / 21

Moving on to step 5:
21 goes into 94 4 times with a remainder of 10.
Put 4 as the next digit of the answer. 
Result so far: 4104.0
Subtracting 84 from 94 leaves us with 10.
Fetch the next digit (5) from the dividend, attach it to 10 and continue: 105 / 21

Step 6:
The number 21 fits into 105 5 times, leaving a remainder of 0.
The number 5 becomes the next digit in our result. 
Result so far: 41045.0
Subtract 105 from 105 to get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Advancing to step 7:
If we divide 0 by 21, we get 0 and a remainder of 0.
Record the quotient 0 as the next digit in the result. 
Result so far: 41045.0
Subtracting 0 from 0 leaves us with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Going ahead to step 8:
If we divide 0 by 21, we get 0 and a remainder of 0.
Record the quotient 0 as the next digit in the result. 
Result so far: 41045.0
Subtracting 0 from 0 leaves us with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

The final result is 41045.0 with a remainder of 0.0.