The average age of Ina,Mina,and Dika is $x$ years. After $y$ years,what will be their average age?

For eliminating $y$ from the equations $3x - 2y = 1$ and $5x + y = 6$,the second equation should be multiplied by

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

$A$ motor boat can travel $30 \, km$ upstream and $28 \, km$ downstream in $7 \, hours$. It can travel $21 \, km$ upstream and return in $5 \, hours$. Find the speed of the boat in still water and the speed of the stream (in $km/h$).

Solve the following pair of linear equations in two variables using the graphical method: $2x + y = 7$ and $x - 2y = 6$.

Do the following equations represent a pair of coincident lines? Justify your answer.
$3x + \frac{1}{7}y = 3$
$7x + 3y = 7$