The general form of a linear equation in two variables is .......... (where,$a^{2}+b^{2} \neq 0$).

Draw the graphs of the equations $x=3, x=5$ and $2x-y-4=0$. Also,find the area of the quadrilateral formed by these lines and the $x$-axis.

Solve the following pairs of equations:
$\frac{1}{2x} - \frac{1}{y} = -1$
$\frac{1}{x} + \frac{1}{2y} = 8, \quad x, y \neq 0$

The cost of $4$ pens and $4$ pencil boxes is $Rs.\, 100$. Three times the cost of a pen is $Rs.\, 15$ more than the cost of a pencil box. Form the pair of linear equations for the above situation. Find the cost of a pen and a pencil box (in $Rs.$).

The graph of the equation ............. passes through the origin.

After $x$ years,the sum of the ages of Sachin and Sehwag will be $y$ years,then the sum of the ages before $3$ years was $\ldots \ldots \ldots \ldots$ years.