I'm trying to figure out the binding energy of 24 Mg. That is (12 protons and 12 neutrons. I keep getting a negative number. Using the equation: Eb (MeV) = (ZMp + NMn - Ma)931.494 MeV/u I should be able to get the right answer but my mass defect ( delta m) is negative. What am I missing? Thank you very much.