well, the principal amount ballooned from 400 to 512, so the interest is the added amount, namely 112 bucks.
[tex]\bf ~~~~~~ \textit{Simple Interest Earned} \\\\ I = Prt\qquad \begin{cases} I=\textit{interest earned}\dotfill&112\\ P=\textit{original amount deposited}\dotfill & \$400\\ r=rate\to 14\%\to \frac{14}{100}\dotfill &0.14\\ t=years \end{cases} \\\\\\ 112=(400)(0.14)t\implies \cfrac{112}{(400)(0.14)}=t\implies 2=t[/tex]
