It is very important to read the question very minutely before going for solving the problem.
Let us assume the unknown number to be = x
Then
4x + = 11
4x = 11 -3
4x = 8
x = 8/4
= 2
So we can see from the above deduction that the unknown number is 2. The correct option among all the options given in the question is option "D". I hope the procedure is clear enough for you to understand.