39991 ÷ 3 = 13330 R1
We're going to perform division on 39991 with 3 as the divisor.

Step 1:
3 goes into 3 1 times with a remainder of 0.
Write down 1 as next digit of of the result. 
Result so far: 1
Subtract 3 from 3 to get 0.
Bring next digit (9) of the dividend behind the 0 and repeat the process: 9 / 3

Step 2:
3 goes into 9 3 times with a remainder of 0.
Write down 3 as next digit of of the result. 
Result so far: 13
Subtract 9 from 9 to get 0.
Bring next digit (9) of the dividend behind the 0 and repeat the process: 9 / 3

Step 3:
3 goes into 9 3 times with a remainder of 0.
Write down 3 as next digit of of the result. 
Result so far: 133
Subtract 9 from 9 to get 0.
Bring next digit (9) of the dividend behind the 0 and repeat the process: 9 / 3

Step 4:
3 goes into 9 3 times with a remainder of 0.
Write down 3 as next digit of of the result. 
Result so far: 1333
Subtract 9 from 9 to get 0.
Bring next digit (1) of the dividend behind the 0 and repeat the process: 1 / 3

Step 5:
3 goes into 1 0 times with a remainder of 1.
Write down 0 as next digit of of the result. 
Result so far: 13330
Subtract 0 from 1 to get 1.

The final result is 13330 with a remainder of 1.