Sarah has $1200.If she invests her money at 4% interest,in how many years will she have $1440? show your work!!

I'm assuming simple interest here

The interest we earn  is 1440 - 1200  =$240

So

I = Prt        Where P = 1200 and r = .04    {4%}

240  = 1200(.04)t   simplify

240 = 48t     divide both sides by 48

240/48 = t = 5 years