The total weight of a father and his son is $70 \, kg$. The weight of the son is one-sixth of the weight of his father. Find the weight of the father and the son.

Solve the following pair of linear equations by the substitution method:
$\sqrt{2} x + \sqrt{3} y = 0$
$\sqrt{3} x - \sqrt{8} y = 0$

Solve the following pair of linear equations by the method of substitution: $2x + 3y = 7$ and $6x + 9y = 23$.

Solve the following pair of linear equations by the substitution method.
$s-t=3$
$\frac{s}{3}+\frac{t}{2}=6$

Form the pair of linear equations for the following problem and find their solution by the substitution method.
$A$ fraction becomes $\frac{9}{11}$ if $2$ is added to both the numerator and the denominator. If $3$ is added to both the numerator and the denominator,it becomes $\frac{5}{6}$. Find the fraction.

For the linear equation in two variables $3x + 2y = 8$,if the value of $x$ is $-2$,then $y = \dots$