Question 853681
The x value will be the same as that of the vertex.  Put the equation into standard form through Completion of the Square.  You can start with the step,
{{{y=-3(x^2+2x)+4}}}
{{{y=-3(x^2+2x+1)+4-(-3)*1}}}
... and YOU should finish this.  


To understand more clearly about standard form and completing the square, see these:


<a href="http://www.algebra.com/tutors/Completing-the-Square-Using-Pictures.lesson?content_action=show_dev">What is Completing the Square</a>
and
<a href="http://www.algebra.com/tutors/Completing-the-Square-to-Solve-General-Quadratic-Equation.lesson?content_action=show_dev">Solving Quadratic Equation using Completing the Square - making standard form </a>