Entropy Questions

The temperature-entropy diagram of a reversible engine cycle is given in the figure. Its efficiency is:

Standard entropy of ${\text{X}}_2$, ${\text{Y}}_2$ and ${\text{XY}}_3$ are $60$, $40$ and $50{\text{J K}}^{-1}{\text{mol}}^{-1}$, respectively. For the reaction $\frac{1}{2}{\text{X}}_2+\frac{3}{2}{\text{Y}}_2\to {\text{XY}}_3$, $\Delta H=-30\text{kJ}$. For the reaction to be at equilibrium, the temperature will be: