Without being given the diffusion constant, I don't see how to express an answer in absolute terms. However you can express it in terms of the diffusion constant. There is no way to calculate the diffusion constant from the information given. It is a characteristic property of the diffusant and diffusing medium. (You can determine D from the flux, or the flux from D. Both are unknowns here. So the best you can do is express the flux in terms of D, and then calculate the total mass moved - in terms of D - from the flux.)