I am having difficulties with a problem that asks for the number of photons per second that are absorbed by a piece of paper. I am given the power of the light source, the distance the source is away from the paper, the wavelength of the light, and the area of the piece of paper. I know that the number of photons per second absorbed can be found by dividing the power by energy of the photons. However, I am not sure how to relate the power of the light source to the distance it is away from the piece of paper and its area. Any help would be greatly appreciated. Thanks a lot!