The given plane has normal vector
Scaling <em>n</em> by a real number <em>t</em> gives a set of vectors that span an entire line through the origin. Translating this line by adding the vector <2, 1, 1> makes it so that this line passes through the point (2, 1, 1). So this line has equation
This line passes through (2, 1, 1) when <em>t</em> = 0, and the line intersects with the plane when
which corresponds the point (3, -1, 1) (simply plug <em>t</em> = 1 into the coordinates of ).
So the distance between the plane and the point is the distance between the points (2, 1, 1) and (3, -1, 1):