$x$ years ago,the age of Mahesh was $y$ years. Then,after $z$ years,his age will be $\ldots$ years.

The solution set of the pair of equations $x+y+1=0$ and $3x+3y+k=0$ is an infinite set. Then $k = \dots$

For what value of $k,$ do the equations $3x - y + 8 = 0$ and $6x - ky = -16$ represent coincident lines?

Pathik travels $600 \, km$ to his home partly by train and partly by car. He takes $8$ hours if he travels $120 \, km$ by train and the rest by car. He takes $20$ minutes longer if he travels $200 \, km$ by train and the rest by car. Find the speed of the train and the car.

Do the equations $4x + 3y - 1 = 5$ and $12x + 9y = 15$ represent a pair of coincident lines? Justify your answer.

For the pair of equations $\lambda x + 3y = -7$ and $2x + 6y = 14$ to have infinitely many solutions,the value of $\lambda$ should be $1$. Is the statement true? Give reasons.