The first order rate constant for the decomposition of CaCO₃ at 700 K is 6.36 $\times$ 10^$-$3s^$-$1 and activation energy is 209 kJ mol^$-$1. Its rate constant (in s^$-$1) at 600 K is x $\times$ 10^$-$6. The value of x is ___________. (Nearest integer)

[Given R = 8.31 J K^$-$ mol^$-$1; log 6.36 $\times$ 10^$-$3 = $-$2.19, 10^$-$4.79 = 1.62 $\times$ 10^$-$5]