Answer
$T_L=-3°C$
Work Step by Step
$\dot{Q}_H=\dot{W}_i+\dot{Q}_L$
Given $\dot{Q}_H=2000\ kW,\ \dot{W}_i=200\ kW$:
$\dot{Q}_L=1800\ kW$
$COP_R=\dot{Q}_L/\dot{W}_i$
$COP_R=9$
$COP_{R,max}=\dfrac{1}{1-\frac{T_L}{T_H}}$
Given $T_H=300\ K$:
$T_L=270\ K=-3°C$
