now, there are 365 (excluding leap years) in a year, so, 275 days is not even a year, but is 275/365 of a year, or 55/73 of a year.
[tex]\bf \qquad \textit{Simple Interest Earned}\\\\
I = Prt\qquad
\begin{cases}
I=\textit{interest earned}\\
P=\textit{original amount deposited}\to& \$1000\\
r=rate\to 4.21\%\to \frac{4.21}{100}\to &0.0421\\
t=years\to \frac{275}{365}\to &\frac{55}{73}
\end{cases}
\\\\\\
I=1000\cdot 0.0421\cdot \cfrac{55}{73}[/tex]
