The negative pion $\left(\pi^{-}\right)$ is an unstable particle with an average lifetime of $2.60 \times 10^{-8} \mathrm{s}$ (measured in the rest frame of the pion). (a) If the pion is made to travel at very high speed relative to a laboratory, its average lifetime is measured in the laboratory to be $4.20 \times 10^{-7} \mathrm{s}$ . Calculate the speed of the pion expressed as a fraction of $c .$ (b) What distance, measured in the laboratory, does the pion travel during its average lifetime?