The equation of a wave motion (with t  in seconds and  x in metres) is given by $\mathrm{y}=7\sin \mathrm{\hspace{0.17em}}\left[7\mathrm{\pi t}-0.4\mathrm{\pi x}+\frac{\mathrm{\pi }}{3}\right]$. The velocity of the wave will be

• A

  17.5 m/s

• B

  $49\mathrm{\pi m}/\mathrm{s}$

• C

  $\frac{49}{2\mathrm{\pi }}\mathrm{m}/\mathrm{s}$

• D

  $\frac{2\mathrm{\pi }}{49}\mathrm{m}/\mathrm{s}$