The number of molecules with energy greater than the threshold energy for a reaction increases five fold by a rise of temperature from  27°C to 42°C. Its energy of activation in KJ/mol is _____. (Take ln 5 = 1.6094; R = 8.314 $\mathrm{J}{\mathrm{mol}}^{-1}{\mathrm{K}}^{-1}$)