If a ball is thrown at 40 m/s and hit back at 50 m/s, and make contact with the bat for 1.2 milliseconds, what is the acceleration

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.