Answer
$T_2=90.31°C$
Work Step by Step
For the stationary insulated constant-volume closed system, the energy balance reduces to:
$-W_e=\Delta U \rightarrow w_e\Delta t=mc_v\Delta T$
For an ideal gas:
$PV=mRT$
Plugging in the values of $P_1=100\ kPa, V_1=48\ m³, T_1=20°C=293.15\ K, R=0.2870\ kJ/kg.K$
$m=57.052\ kg$
With $w_e=0.1\ kW, \Delta t =8h=28800s, c_v=0.718\ kJ/kg.K$
We get to $\Delta T=70.31°C$, hence $T_2=90.31°C$
