According to the question
$\frac{1}{{2l}}\sqrt {\frac{{160}}{{\rm{m}}}} - \frac{1}{{2l}}\sqrt {\frac{{129.6}}{{\rm{m}}}} = 10$
$\frac{1}{{2l}}\sqrt {\frac{{10}}{m}} [4 - 3.6] = 10 \Rightarrow \frac{1}{{2l}}\sqrt {\frac{{10}}{m}} = 25$
so ${{\rm{V}}_{{\rm{TF}}}} = \frac{1}{{2l}}\sqrt {\frac{{160}}{{\rm{m}}}} = 4\left[ {\frac{1}{{2l}}\sqrt {\frac{{10}}{{\rm{m}}}} } \right] = 100\,{\rm{Hz}}$

$(A)$ a high-pressure pulse starts traveling up the pipe, if the other end of the pipe is open.
$(B)$ a low-pressure pulse starts traveling up the pipe, if the other end of the pipe is open.
$(C)$ a low-pressure pulse starts traveling up the pipe, if the other end of the pipe is closed.
$(D)$ a high-pressure pulse starts traveling up the pipe, if the other end of the pipe is closed.
