You can put this solution on YOUR website! The given directrix indicates the line of symmetry is horizontal. Having the focus (1, 4) and the directrix x=-3, means you can use the Distance Formula according to the definition for a parabola and derive this equation. The parabola is some variable set of points, (x,y). The directrix is some variable set of points, (-3, y). Drawing a picture will help.
Starting with your symbolic statement, , using Distance Formula;
Simplify that and form your result into x on one side, and the expression of y on the other side.