Any point on the $y$-axis is of the form

Find the common solution of the equations $x + y = 0$ and $x - y = 0$.

Express the following linear equation in the form $ax + by + c = 0$ and indicate the values of $a, b,$ and $c$ in each case:
$\pi x - 3y = 18$

How many solution$(s)$ of the equation $2x + 1 = x - 3$ are there on the:
$(i)$ Number line
$(ii)$ Cartesian plane

How many linear equations in $x$ and $y$ can be satisfied by $x = 1$ and $y = 2$?

Write whether the following statements are True or False? Justify your answers.
$(i)$ The line parallel to the $y$-axis at a distance of $4$ units to the left of the $y$-axis is given by the equation $x = -4$.
$(ii)$ The graph of the equation $y = mx + c$ passes through the origin.