Equations of lines - an introduction
Equations like x + y = 4 and 2x - 3y = 6 are called linear equations because if you plot the possible solutions they will be on same line.
You can move the slider to change the value of the x coordinate of the point - you see that each pair of values works when you substitute them into the equation. Try it and see. Using the other sliders you can try a few different lines.