The phase difference between two points is related to the wave velocity by the equation:
\[
\Delta \phi = \frac{2 \pi \Delta x}{\lambda}
\]
where \( \Delta \phi = \frac{\pi}{4} \), and the separation \( \Delta x = 1.25 \, \text{cm} = 0.0125 \, \text{m} \).
The wavelength \( \lambda \) can be found using the wave velocity formula:
\[
v = f \lambda
\]
Thus, the wave velocity is calculated to be 100 m/s.