Answer
$y^{2}= -16x$
Work Step by Step
Given: The equation of directrix is $x=-p=4$
This gives: $p=-4$
This shows that the parabola opens to the right.
The general form of the equation of a parabola which opens to the right is
$y^{2}= 4px$
Thus, the equation of the parabola becomes:
$y^{2}= 4(-4)x$
$\implies y^{2}= -16x$
