3991 ÷ 4 = 997 R3
Let's divide 3991 by 4.

Step 1:
4 goes into 3 0 times with a remainder of 3.
Write down 0 as next digit of of the result. 
Result so far: 0
Subtract 0 from 3 to get 3.
Bring next digit (9) of the dividend behind the 3 and repeat the process: 39 / 4

Step 2:
4 goes into 39 9 times with a remainder of 3.
Write down 9 as next digit of of the result. 
Result so far: 9
Subtract 36 from 39 to get 3.
Bring next digit (9) of the dividend behind the 3 and repeat the process: 39 / 4

Step 3:
4 goes into 39 9 times with a remainder of 3.
Write down 9 as next digit of of the result. 
Result so far: 99
Subtract 36 from 39 to get 3.
Bring next digit (1) of the dividend behind the 3 and repeat the process: 31 / 4

Step 4:
4 goes into 31 7 times with a remainder of 3.
Write down 7 as next digit of of the result. 
Result so far: 997
Subtract 28 from 31 to get 3.

The final result is 997 with a remainder of 3.