This is the 2nd video in the "What to eat for breakfast?" series. In this video, we demonstrate 1) how to verify a given ordered 2-tuple is a solution to a given linear equation; 2) how to visualize the set of solutions to a given linear equation about two unknowns in the x-O-y plane; 3) present the fact that a linear equation about two unknowns has infinitely many solutions. In fact, the set of its solutions contains all the ordered 2-tuples that correspond to points on a certain straight line. (video link needs to be updated. then add more tags)