Subject: Last question on today's quiz

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The point on the plane is:

 Q = (0, 0, -6)

 which means its 6 units BEHIND the screen

 The viewpoint is at:

  V = (4, 2, 2)

  Which means its 2 units in FRONT of the screen.
  (and offset 4 to the left and 2 above the origin)

Since the ray direction is (0, 0, -1) the x and y coordinates of
points on the ray are the SAME as at the viewpoint so the hitpoint
is

  H = (4, 2, -6)

  and the distance is

  t = 8