Answer
$$1.2 \times 10^{2} \mathrm{cm} / \mathrm{s}
$$
Work Step by Step
Every traveling wave has an angular frequency of $$\omega=40 \pi \mathrm{rad} / \mathrm{s}$$ and an angular wave number of $$k=\pi / 3 \mathrm{cm}^{-1} .$$ Therefore wave speed is
$$
v=\omega / k=(40 \pi \mathrm{rad} / \mathrm{s}) /\left(\pi / 3 \mathrm{cm}^{-1}\right)=1.2 \times 10^{2} \mathrm{cm} / \mathrm{s}
$$
