We look at the division of 643521 by 158 
Our goal is to divide 643521 by 158.

On to step 1:
158 goes into 6 0 times with a remainder of 6.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Deduct 0 from 6 and we're left with 6.
Bring next digit (4) of the dividend behind the 6 and repeat the process: 64 / 158

Let's proceed to step 2:
158 goes into 64 0 times with a remainder of 64.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtracting 0 from 64 leaves us with 64.
Include the next digit (3) from the dividend after 64, then repeat: 643 / 158

Step 3:
158 can be fit into 643 4 times, resulting in a remainder of 11.
The number 4 becomes the next digit in our result. 
Result so far: 4.0
If we take 632 away from 643, we end up with 11.
Bring next digit (5) of the dividend behind the 11 and repeat the process: 115 / 158

Step 4:
If we divide 115 by 158, we get 0 and a remainder of 115.
Put 0 as the next digit of the answer. 
Result so far: 40.0
The remainder is 115 after subtracting 0 from 115.
Fetch the next digit (2) from the dividend, attach it to 115 and continue: 1152 / 158

Moving on to step 5:
158 goes into 1152 7 times with a remainder of 46.
Put 7 as the next digit of the answer. 
Result so far: 407.0
If we subtract 1106 from 1152, we get 46.
Bring next digit (1) of the dividend behind the 46 and repeat the process: 461 / 158

On to step 6:
When dividing 461 by 158, we get 2 with a remainder of 145.
The next digit of our result is 2. 
Result so far: 4072.0
If we take 316 away from 461, we end up with 145.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1450, and continue the process.

Moving on to step 7:
158 can be fit into 1450 9 times, resulting in a remainder of 28.
The next digit of our result is 9. 
Result so far: 4072.9
Subtract 1422 from 1450 to get 28.
Since there are no more digits in the dividend, we add a zero to the remainder making it 280, and continue the process.

Let's proceed to step 8:
158 can be fit into 280 1 times, resulting in a remainder of 122.
Write down 1 as next digit of the result. 
Result so far: 4072.91
The remainder is 122 after subtracting 158 from 280.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1220, and continue the process.

Let's proceed to step 9:
When dividing 1220 by 158, we get 7 with a remainder of 114.
Use 7 as the next digit of our solution. 
Result so far: 4072.917
If we subtract 1106 from 1220, we get 114.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1140, and continue the process.

Let's proceed to step 10:
When dividing 1140 by 158, we get 7 with a remainder of 34.
Put 7 as the next digit of the answer. 
Result so far: 4072.9177
If we take 1106 away from 1140, we end up with 34.
Since there are no more digits in the dividend, we add a zero to the remainder making it 340, and continue the process.

The final outcome is 4072.9177, with a leftover of 0.00034.