The reaction Cis $-\mathrm{X}\rightleftharpoons \mathrm{tran}-\mathrm{X}$ is 1st order in both directions. At 25° C, the equilibrium constant is 0.10 and the rate constant $k_f=3\times {10}^{-4}{\sec }^{-1}\text{. }$In an experiment starting with the pure cis form, bow long will it take for half of the equilibrium amount of the trans isomer to be formed?