Express the following linear equation in the form $a x+b y+c=0$ and indicate the values of $a, b$ and $c$ in each case

$\pi x-3 y=18$

Draw the graphs of linear equations $y=x$ and $y=-x$ on the same cartesian plane.

What do you observe?

If $(2,3)$ is a solution of the equation $7 x-3 y=a$ and $(a, a+1)$ is a solution of the equation $2 x+y=b,$ find the values of $a$ and $b$

The graph of the linear equation $y = x$ passes through the point.

If the graph of equation $3 x+a y=7$ passes through the point $(3,-1),$ then the value of $a=\ldots \ldots \ldots$