Solve the following pair of linear equations by the substitution method.
$3x - y = 3$
$9x - 3y = 9$

(D) Given equations are:
$3x - y = 3$ $...(1)$
$9x - 3y = 9$ $...(2)$
From equation $(1)$,we can express $y$ in terms of $x$:
$y = 3x - 3$ $...(3)$
Substituting the value of $y$ from equation $(3)$ into equation $(2)$:
$9x - 3(3x - 3) = 9$
$9x - 9x + 9 = 9$
$9 = 9$
Since $9 = 9$ is a true statement for all values of $x$,the two equations are coincident lines.
Therefore,the given pair of linear equations has infinitely many solutions.
The relationship between the variables is given by $y = 3x - 3$.