Let h be a solid hemisphere of radius a where the density at any point is proportional to the distance from the center of the base.
(a) find the mass of h.
(b) find the center of mass of h.
(c) find the moment of inertia of h about its axis.

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when it gains or loses electrons

heats surface water up

you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m