What would be the energy (eV) of a gamma ray photon with the wavelength h (Planck's length)?
Have you tried to look it up? ##h## usually denotes the Planck constant which is not a length. Do you know the two formulas, that connect the energy with the frequency and the frequency with the wavelength of electromagnetic waves?
What's the 2nd?
The relationship between the wavelength and the frequency. (As an aside, this one is true for all waves of all types, not just light).
You have the one that lets you calculate the energy from the frequency, so if you can just get the frequency from the wavelength you'll be able to get the energy from the wavelength.
So what's the formula?
What does frequency stand for, and what is wavelength?
Frequency: number of occurrences/time unit (Hz)
Wavelength: distance between the peaks of a wave (nm)
Now what's the formula?
Thus the propagation velocity is distance between peaks times peaks per seconds. In case of light it is ##c=\lambda \cdot f\,.## With ##c## being constant, you can calculate one from the other. With the energy formula you have all what's needed.
Separate names with a comma.