A loudspeaker is positioned at the open end of a tube that is closed and contains powder. When the loudspeaker emits sound at frequency $1200\,\text{Hz}$, a stationary wave forms in the tube. The powder collects at the nodes of the stationary wave, as shown. The speed of sound in air is $336\,\text{m s}^{-1}$. What is the value of distance $x$?
- A$28\,\text{cm}$
- B$42\,\text{cm}$
- C$84\,\text{cm}$
- D$112\,\text{cm}$