Four years ago,the sum of the ages of four persons was $40$ years. After two years,the sum of the ages of the same four persons will be ............ years.

Solve the following pairs of equations by the cross-multiplication method:
$x - 3y = -5$
$3x = 7y - 13$

$A$ boat goes $32 \, km$ upstream and $36 \, km$ downstream in $7$ hours. In $9$ hours,it can go $40 \, km$ upstream and $48 \, km$ downstream. Determine the speed of the stream and that of the boat in still water. (Speed of boat in still water is more than the speed of the stream of river.)

If $x+1$ is a factor of $2x^{3}+ax^{2}+2bx+1$,then find the values of $a$ and $b$ given that $2a-3b=4$.

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.

The solution set of the pair of equations,$x=1$ and $y=2$ is ..........