well, 21 months is really more than 1 year, since there are 12 months in a year, 21 months is actually 21/12 years.
[tex]\bf ~~~~~~ \textit{Simple Interest Earned} \\\\ I = Prt\qquad \begin{cases} I=\textit{interest earned}\\ P=\textit{original amount deposited}\dotfill & \$1620\\ r=rate\to 5.3\%\to \frac{5.3}{100}\dotfill &0.053\\ t=years\to \frac{21}{12}\dotfill &\frac{7}{4} \end{cases} \\\\\\ I=(1620)(0.053)\left( \frac{7}{4} \right)\implies I=150.255[/tex]
