What is the equation of a parabola with vertex at the origin and a directrix of x = -3?

_{
}(A) x =

_{
}(B) x =

_{
}(C) y =

_{
}(D) y =

x = - p

x = -3

p = 3

4xp = y^{2}

4(3)x = y^{2}

12x = y^{2}

x =