Alright guys Im looking for some help with this problem regarding calculating total electric charge in a layer of ions. This layer of ions is bounded between the planes x+2y+2z=4 and x+3y+3z=3, and by the 3 co-ordinate planes. The density of the ions is rises linearly from zero at the outer plane ( x+2y+2z=4) and increases linearly to 10^15 at the inner plane (x+3y+3z=4). Furthermore, the surface charge density is constant in planes parallel to the planes x+2y+2z=4 and x+3y+3z=4. I see that in order to calculate the total electric charge I must compute a triple integral of the charge density, however I'm trying to find an expression for the charge density function. Could anybody help me with writing density (as a function of x,y,z) based upon the information given in the first paragraph? Not looking for the final answer here, just some instruction. Thank you :) PS. I wasn't sure whether this should be posted here or in the electrical section, sorry just in case.