When a plane does not pass through the origin, performing operations on vectors whose bodies lie in it is more complicated than when the plane passes through the origin. Consider the picture in this subsection of the plane

and the three vectors with endpoints (2, 0, 0), (1.5, 1, 0), and (1.5, 0, 1).
(a) Redraw the picture, including the vector in the plane that is twice as long as the one with endpoint (1.5, 1, 0). The endpoint of your vector is not (3, 2, 0), what is it?
(b) Redraw the picture, including the parallelogram in the plane that shows the sum of the vectors ending at (1.5, 0, 1) and (1.5, 1, 0). The endpoint of the sum, on the diagonal, is not (3, 1, 1), what is it?

0.5 -0.5