1. The problem statement, all variables and given/known data Knowing the Z (number of protons) of an element, how can I find N (number of neutrons) or A (mass number) of the element? 2. Relevant equations I tried to use the semi-empirical mass formula EB = ανΑ - αsA2/3 - αcZ2/A1/3 - αΑ(Α-2Ζ)2/Α - δ(Α,Ζ) for this. 3. The attempt at a solution I tried to to find the maximum binding energy by dEb/dA=0 for a given Z number. I came to the following equation where I substituted Z=32 as an example for Germanium: 2113.9 A2 - 11.4 A4/3 + 352.16 A2/3 + 67665.92 = 0 Now I can't find a way to solving for A. Only way to find A that I can see is by substituting numerically values for A and see when the equation is valid.