Answer
$v=360m/s$
Work Step by Step
For an open-closed tube, harmonic frequencies are found using the formula $$f_n=\frac{nv}{4L}$$ for odd values of $n$. The third lowest harmonic is the third lowest odd integer, which is 5. Therefore, $n=5$. Solving for $v$ in the equation yields $$v=\frac{4Lf_n}{n}$$ Substituting known values yield $$v=\frac{4(0.60m)(750Hz)}{5}=360m/s$$
