# How many protons and neutrons are in uranium-235?

The atomic number, $Z$, of any element, is the number of protons, positively charged nuclear particles, contained in the nucleus. The mass number ($235$) is the sum of the number of protons, AND the number of neutrons, NEUTRALLY charged nuclear particles. Note that only protons and neutrons contribute to atomic mass to any degree.
You have ""^235U. If $Z = 92$ how many neutrons are there? And how did I know $Z = 92$?