The heat (energy) needed to raise the temperature of the water is given by

The wavelength of the radiation of the oven is

, so the energy of a single photon of this radiation is

So, the number of photons required to heat the water is the total energy absorbed by the water divided by the energy of a single photon:

photons
A advantage is less car accidents and a disadvantage is, in order to keep the roads clear of ice is a chemical. Like salt. Which is bad for the animals.
Explanation:
Attachments of the solution are below.