Answer
$ 48.04\%$
Work Step by Step
The simple interest on an investment (or loan) of PV dollars at an annual interest rate of r for a period of t years is $INT=PVrt$.
The investment was made with $PV=255.96$,
the time of investment was t= 6 months = 0.5 years,
and the $FV=317.44$
With $INT=FV-PV$, we solve
$INT=PVrt\ \ \ \ $ for r, (divide both sides with $PV\cdot t$)
$ r=\displaystyle \frac{FV-PV}{PV\cdot t}=\frac{317.44-255.96}{255.96\cdot 0.5}\approx$0.480387560556,
to the nearest $0.01\%,$
$ 48.04\%$
