Find solution of a pair of linear equations in two variables by elimination method: 

$2x+3y=0$

$3x+4y=5$.

Solve the following system of linear equations:

$2x-3y=13$

$7x-2y=20$

Solve the following system of linear equations:

$x+y=3$

$4x-3y=26$

The population of Patna city is $96000$, the decreasing rate of population is $800$ per year. Population of Patliputra is $68000$, the increasing rate of population is $1200$ per year. In how many years will the population of both places be equal?

$5$years ago, I was three times as old as my son. Ten years hence, I will be twice as old as my son. Find my present age and my son's present age.