The displacement $y$ of a wave travelling in the $x$-direction is given by $y = 10^{-4}\sin\left(600t - 2x + \frac{\pi}{3}\right)$ metres where x is expressed in metres and t in seconds. The speed of the wave-motion, in $\mathrm{ms}^{-1}$, is\\
(1) 300\\
(2) 600\\
(3) 1200\\
(4) 200