6000 kg train moving 5 m/sec to east collides with 5000 kg train moving 3 m/sec to west. what is their velocity

The first-order reaction a→2b+c has rate constant 0.538 s−1. if the initial concentration of a is 0.867 mol l−1, what is the half-life of the reaction in seconds? remember to use correct significant figures in your answer (round your answer to the nearest hundredth). do not include units in your response.