Two years ago,Salim was thrice as old as his daughter and six years later,he will be four years older than twice her age. How old are they now? (in $year$)

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.

If $x=a$ and $y=b$ is the solution of the equations $x-y=2$ and $x+y=4,$ then the values of $a$ and $b$ are,respectively:

The solution of the pair of equations $x+2=0$ and $y-1=0$ is $(x, y) = \dots$

Find the value$(s)$ of $p$ and $q$ for the pair of equations $2x + 3y = 7$ and $2px + py = 28 - qy$ if they have infinitely many solutions.

Solve the following pair of equations by the cross-multiplication method:
$ax - by = \frac{a-b}{2}$
$x + 3y = 2$