The atomic mass of an element is equal to the:
atomic number
o number of protons
number of protons and neutrons
o mass of protons, neutrons, and electrons

The answer should be the third option "number of protons and neutrons." The atomic mass of a element is equal to the amount of protons, and neutrons added together in that element. So for example if we are trying to find the atomic mass of hydrogen you would add the total amount of protons and neutrons together to find it's mass although it doesn't equal the exact amount of it's mass but it's close.

Hope this helps.