Relating Gibbs Free Energy to Equilibrium Constants
To solve this problem, you suppose that $\Delta$$H°$  and $\Delta$$S°$ do not change with temperature. You calculate $\Delta$$G°$ by two approaches : $1)$ - $RT$ ln $K_p$, and $2)$ $\Delta$$H°$ - $T\Delta$$S°$. Then $T$ can be easily obtained.