Question 682742
Nina is currently three times as old as her sister Tina. 

let {{{x}}} be Nina’s age  and {{{y}}}  Tina’s age

currently {{{x=3y}}}.....eq. 1

In four years, Nina will only be twice as old as Tina.

 
{{{x+4=2(y+4)}}}.....eq. 2.....plug in {{{x=3y}}}


{{{3y+4=2(y+4)}}}....solve for {{{y}}}

{{{3y+4=2y+8}}}

{{{3y-2y=8-4}}}

{{{y=4}}}.......Tina’s current age

{{{x=3y}}}...=>...{{{x=3*4}}}...=>...{{{x=12}}}......Nina’s current age