The equation of a stationary wave is given by
$y = 6 \sin \left(\frac{\mathrm{\pi x}}{3}\right)\cos 40\mathrm{\pi t}$

where y and x are given in cm and time t in second, the separation between two consecutive antinodes is:

• A

  3 cm

• B

  6 cm

• C

  12 cm

• D

  20 cm