Answer
201.6 K
Work Step by Step
Efficiency $\eta=\frac{\text{work done}}{\text{heat withdrawn}}=\frac{0.71\,kJ}{2.71\,kJ}=0.262$
Another equation for the efficiency is
$\eta=1-\frac{T}{T_{h}}=\frac{T_{h}-T}{T_{h}}$
where $T$ is the temperature of the cold sink and $T_{h}$ is the temperature of the hot source.
As the temperature of water at the triple point is equal to $273.16\,K$, we have
$T_{h}=273.16\,K$ and
$\eta=0.262=\frac{273.16\,K-T}{273.16\,K}$
$\implies T=273.16\,K-(0.262\times273.16\,K)=201.6\,K$
