Using Einstein's photoelectric equation $\frac{hc}{\lambda} = \frac{hc}{\lambda_0} + \frac{1}{2}mv^2$, we can set up simultaneous equations using the given pairs of wavelengths and velocities. Note that the velocity values in the table are interpreted as $v \times 10^5$ m/s (or $v \times 10^7$ cm/s) to yield physically consistent results for Planck's constant. By subtracting the equations for different wavelengths, the threshold work function term cancels out, allowing us to solve for $h$. Substituting $h$ back into one of the equations gives the threshold wavelength $\lambda_0$.