Need some help with questions like this. I'm quite confused as to how to answer it in general. http://tinypic.com/view.php?pic=2rhu6f7&s=6 I've posted only the first first basic problem as I can do the rest if I understand the logic behind this. I actually encountered this while I was studying the introduction to linear algebra system of linear equations chapter. What do "s" and "t" represent in this?