Solve the following pairs of equations by the method of elimination:
$9x + 7y = 55$
$7x + 9y = 57$

For which value$(s)$ of $\lambda$,do the pair of linear equations $\lambda x + y = \lambda^2$ and $x + \lambda y = 1$ have:
$(i)$ no solution?
$(ii)$ infinitely many solutions?
$(iii)$ a unique solution?

There are some students in the two examination halls $A$ and $B$. To make the number of students equal in each hall,$10$ students are sent from $A$ to $B$. But if $20$ students are sent from $B$ to $A$,the number of students in $A$ becomes double the number of students in $B$. Find the number of students in the two halls.

The solution of a pair of equations $y+x=2$ and $y-x=4$ is $(x, y)=\ldots \ldots \ldots . . .$

Draw the graph of the pair of equations $2x + y = 4$ and $2x - y = 4$. Write the vertices of the triangle formed by these lines and the $y$-axis. Also,find the area of this triangle.

Rajvansh invested some amount at the rate of $12 \%$ simple interest and some amount at the rate of $10 \%$ simple interest. He received a yearly interest of Rs. $130$. However,if he had interchanged the amounts invested,he would have received Rs. $4$ more as interest. How much amount did he invest at each rate?