Planck's constant and a wavelength in code

You will fit a straight line to stopping potentials, as Millikan did, and find a de Broglie wavelength.

The idea. The graph of $V_0$ against $\nu$ is a straight line of slope $h/e$. The best slope for points $(x, y)$ is $\dfrac{n\sum xy - \sum x \sum y}{n\sum x^2 - (\sum x)^2}$. A moving particle has the wavelength $h/(mv)$.

Your tasks.

1. In slope, return the best-fit slope of volts against freqs.
2. In planck, return Planck's constant in J s from a slope in V s. Take $e = 1.6 \times 10^{-19}$ C.
3. In de_broglie, return the wavelength in m of a particle of mass mass in kg moving at speed in m/s. Take $h = 6.63 \times 10^{-34}$ J s.