A modest answer.
Here is a way to explain equations of straight line at $\approx$ 7th grade.
The points on the graphics below look aligned. Could you find a common property to all the displayed coordinates $(x,y)$ ? Sooner or later, one finds $x+y=2$ (btw, simpler to catch than $y=-x+2$). Let us understand why all that. A reason is that if I increase $x$ by one, I have to decrease $y$ by one in order to preserve the common property $x+y=2$, or I can increase $x$ by 2 and decrease $y$ by 2, inviting your audience to follow the moving point with a finger. This way helps in capitalizing basic linearity concepts with a natural correspondence betwen an algebraic property and a geometric property. In particular, the slope concept has been gently introduced. Then we can switch to other examples...
Back to your problem, assume you are given a straight line with equation $2x+3y=6$, that is due to cut the axes, if you do for example $y=0$ (imposing thus $2x=6$, meaning $x=3$), then you have the point $(x=3,y=0)$ which is the unique point of interection with the $x$-axis. One can do the same for $y$-axis of course.
