Some operators are missed.
Any way I can guess that the function is x^2+6x+3
To find the vertex form of the equation you need to form a perfect square.
To do that add and subtract 9:
x^2 + 6x + 9 +3 - 9 = (x^2+6x+9) + (3-9) = (x+3)^2 -6
Answer: f(x) = (x+3)^2 - 6
