Question

$9$ years later, a girl will be $3$ times an old as she was $9$ years ago. How old is she now?

Answer 1

Let the girl age be $x$

After $9$ years her age will be $x+9$

Before $9$ years her age will be $x-9$

$\Rightarrow x+9=3(x-9)$

$\Rightarrow x+9=3x-27$

$\Rightarrow x-3x=-27-9$

$\Rightarrow -2x=-36$

$\therefore x=18$

Girl' s age is $18$ years.