For a reversible reaction $\mathrm{A} \rightleftharpoons \mathrm{B}$, the $\Delta \mathrm{H}_{\text {forward reaction }}=20 \mathrm{~kJ} \mathrm{~mol}^{-1}$. The activation energy of the uncatalysed forward reaction is $300 \mathrm{~kJ} \mathrm{~mol}^{-1}$. When the reaction is catalysed keeping the reactant concentration same, the rate of the catalysed forward reaction at $27^{\circ} \mathrm{C}$ is found to be same as that of the uncatalysed reaction at $327^{\circ} \mathrm{C}$. The activation energy of the catalysed backward reaction is $\_\_\_\_$ kJ $\mathrm{mol}^{-1}$.