How many unit tiles need to be added to the expression

x2 + 4x + 3 in order to form a perfect square trinomial

The answer to your question would be 1.

In the question "How many unit tiles need to be added to the expression x2 + 4x + 3 in order to form a perfect square trinomial" the correct answer is 1 unit tile. Because, to make the expression x^2 + 4x + 3 a perfecr square trinomial we have x^2 + 4x + 3 + 1 = x^2 + 4x + 4 = (x + 2) ^2