Step 1: Understanding the Question:
We need to find the equation of a 3D plane that is perfectly parallel to the standard XY plane and passes through a specific coordinate point $(7, 8, 6)$.
Step 2: Key Formula or Approach:
The standard equation of the XY plane is $z = 0$, because every single point on the XY plane has a height (z-coordinate) of zero.
Any plane that is parallel to the XY plane will have a constant z-coordinate for all its points. Its general equation is simply $z = c$, where $c$ is a constant.
Step 3: Detailed Explanation:
Since the required plane is parallel to the XY plane, its equation must be of the form $z = c$.
We are given that the plane passes through the point $A(x_1, y_1, z_1) = (7, 8, 6)$.
Because the point lies on the plane, its z-coordinate must satisfy the plane's equation.
Therefore, we plug the z-coordinate of point A into our general equation:
$c = 6$
This means the equation of the entire plane is just $z = 6$.
Step 4: Final Answer:
The Cartesian equation of the plane is $z = 6$, which corresponds to option (D).