Answer
Please see the work below.
Work Step by Step
We know that for an adiabatic process
$T_2V_2^{\gamma-1}=T_3V_3^{\gamma-1}$
We plug in the known values to obtain:
$(273)(\frac{1}{3})^{\frac{7}{5}-1}=T_3(\frac{1}{5})^{\frac{7}{5}-1}$
$T_3=335K$
