A wave is represented by the equation $\mathrm{y}=7\sin (7\mathrm{\pi t}-0\cdot 04\mathrm{x}+\mathrm{\pi }/3)$ where x is in metre and t in second. The speed of the
wave is

• A

  $175\pi m/s$

• B

  $\left(49\mathrm{\pi }\right)\mathrm{m}/\mathrm{s}$

• C

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

• D

  $(0\cdot 28\mathrm{\pi })\mathrm{m}/\mathrm{s}$