What is the equation of a parabola with vertex (0 0) and directrix x -3.?

The equation of a parabola with vertex at (0, 0) and a directrix of ( x = -3 ) opens to the right, as the directrix is a vertical line. The distance from the vertex to the directrix is 3 units. The standard form of the equation for a horizontally-opening parabola is given by ( y^2 = 4px ), where ( p ) is the distance from the vertex to the directrix. Therefore, with ( p = 3 ), the equation is ( y^2 = 12x ).