86521007 ÷ 866 
We're looking to find how many times 866 goes into 86521007.

Step 1:
The number 866 fits into 8 0 times, leaving a remainder of 8.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we take 0 away from 8, we end up with 8.
Include the next digit (6) from the dividend after 8, then repeat: 86 / 866

Step 2:
866 can be fit into 86 0 times, resulting in a remainder of 86.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 86 to get 86.
Include the next digit (5) from the dividend after 86, then repeat: 865 / 866

Let's proceed to step 3:
If we divide 865 by 866, we get 0 and a remainder of 865.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Deduct 0 from 865 and we're left with 865.
Fetch the next digit (2) from the dividend, attach it to 865 and continue: 8652 / 866

Going ahead to step 4:
The number 866 fits into 8652 9 times, leaving a remainder of 858.
Use 9 as the next digit of our solution. 
Result so far: 9.0
If we subtract 7794 from 8652, we get 858.
Take the next digit (1) from the dividend and append it to 858, then repeat: 8581 / 866

Step 5:
8581 divided by 866 is 9 with a remainder of 787.
The next digit of our result is 9. 
Result so far: 99.0
Deduct 7794 from 8581 and we're left with 787.
Grab the next digit (0) from the dividend, add it to 787, then carry on: 7870 / 866

Step 6:
866 goes into 7870 9 times with a remainder of 76.
Use 9 as the next digit of our solution. 
Result so far: 999.0
If we subtract 7794 from 7870, we get 76.
Fetch the next digit (0) from the dividend, attach it to 76 and continue: 760 / 866

Moving on to step 7:
760 divided by 866 is 0 with a remainder of 760.
Record the quotient 0 as the next digit in the result. 
Result so far: 9990.0
If we subtract 0 from 760, we get 760.
Append the next digit (7) from the dividend to 760 and continue with: 7607 / 866

Advancing to step 8:
866 can be fit into 7607 8 times, resulting in a remainder of 679.
Record the quotient 8 as the next digit in the result. 
Result so far: 99908.0
Subtracting 6928 from 7607 leaves us with 679.
Since there are no more digits in the dividend, we add a zero to the remainder making it 6790, and continue the process.

Going ahead to step 9:
If we divide 6790 by 866, we get 7 and a remainder of 728.
Use 7 as the next digit of our solution. 
Result so far: 99908.7
If we subtract 6062 from 6790, we get 728.
Since there are no more digits in the dividend, we add a zero to the remainder making it 7280, and continue the process.

On to step 10:
866 can be fit into 7280 8 times, resulting in a remainder of 352.
The number 8 becomes the next digit in our result. 
Result so far: 99908.78
Subtract 6928 from 7280 to get 352.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3520, and continue the process.

On to step 11:
The number 866 fits into 3520 4 times, leaving a remainder of 56.
The next digit of our result is 4. 
Result so far: 99908.784
Subtracting 3464 from 3520 leaves us with 56.
Since there are no more digits in the dividend, we add a zero to the remainder making it 560, and continue the process.

Moving on to step 12:
The number 866 fits into 560 0 times, leaving a remainder of 560.
The number 0 becomes the next digit in our result. 
Result so far: 99908.784
The remainder is 560 after subtracting 0 from 560.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5600, and continue the process.

Advancing to step 13:
866 goes into 5600 6 times with a remainder of 404.
Put 6 as the next digit of the answer. 
Result so far: 99908.78406
Subtracting 5196 from 5600 leaves us with 404.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4040, and continue the process.

Step 14:
4040 divided by 866 is 4 with a remainder of 576.
The number 4 becomes the next digit in our result. 
Result so far: 99908.784064
Subtract 3464 from 4040 to get 576.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5760, and continue the process.

Advancing to step 15:
The number 866 fits into 5760 6 times, leaving a remainder of 564.
Put 6 as the next digit of the answer. 
Result so far: 99908.7840646
If we subtract 5196 from 5760, we get 564.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5640, and continue the process.

Going ahead to step 16:
The number 866 fits into 5640 6 times, leaving a remainder of 444.
Use 6 as the next digit of our solution. 
Result so far: 99908.78406466
Subtract 5196 from 5640 to get 444.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4440, and continue the process.

After the division, we end up with 99908.78406466 and a remainder of 4.44e-07.