The diagram represents a stationary wave on a string at two moments when the vertical displacement is greatest. The distance shown is 90 cm. The wave has a frequency of $12\,\text{Hz}$. What is the wave speed?
- A$3.6\,\text{m s}^{-1}$
- B$7.2\,\text{m s}^{-1}$
- C$360\,\text{m s}^{-1}$
- D$720\,\text{m s}^{-1}$