You can put this solution on YOUR website!
First draw the graph:
Pick a couple values for x and then solve for y for each. That gives you two points to plot, then you can connect the lines. I chose 4 and 8 giving me y values of 1/2 and 7/2. My points were therefore (4,1/2) and (8,7/2). The graph looks like this:
Now, plot the two points given in the question, namely (2,-1) and (-1,2) and it is clear that neither is on the line.
To provide the algebraic justification, take the x value from the first point, namely 2, and the y value from that same point, namely -1 and substitute those values into the equation.
. Since the two values for the first point do not make the equation statement true, the point cannot lie on the line.
You should be able to solve part b yourself now.