[tex]\begin{gathered} P=\text{PRINCIPAL}=400 \\ r=\text{interest rate 5\% anual=0.05} \\ t=time=6years \\ \text{the simple interest formula is } \\ I=\text{Prt} \\ IN\text{ THIS CASE} \\ I=(400)(0.05)(6) \\ I=120 \\ \text{hence, in 6 years, Donald will have 400+120=520 dollars in his account.} \end{gathered}[/tex]
