Confused on how to get the answer

Question

Neon (₁₀Ne) has three stable isotopes with consecutive mass numbers. Write the complete nuclear symbol (with neutron number) for each.

Answer 1

Nuclear symbols are given in the form ^A_ZX, where A is the mass number (protons + neutrons), Z is the atomic number (just protons, which determines the identity of the element) and X, it's name.

All species of Neon have Z = 10 protons.

The most common has 10 neutrons, for an "A" of 20.

The other two (though there are more) have 21 (< 1%) and 22 (~10%)