How to get the cartesian form of a plan from its Hesse form?

Question

This class provides the necessary tools to find a plane in a point cloud using the RANSAC algorithm; the plane is defined in Hesse normal form, meaning that it returns an array of four cells: the first three cells correspond to the three components of the normal vector of the plane ($ \vec{n} = [ x, y, z ] $) and the fourth one is the distance of the plane from the origin. How can I use that result to get the equation of the plane under the form $ ax + by + cz - d = 0 $ ? Otherwise, how could I tell if a point belongs to the plane while in Hesse form? Thank you in advance for your answer.