keeping in mind that a year has 12 months, thus 9 months are really 9/12 of a year, so
[tex]~~~~~~ \textit{Simple Interest Earned} \\\\ I = Prt\qquad \begin{cases} I=\textit{interest earned}\\ P=\textit{original amount deposited}\dotfill & \pounds 1640\\ r=rate\to 4.5\%\to \frac{4.5}{100}\dotfill &0.045\\ t=years\to \frac{9}{12}\dotfill &\frac{3}{4} \end{cases} \\\\\\ I = (1640)(0.045)(\frac{3}{4})\implies I=55.35[/tex]
