No diagram is given therefore I cannot answer however, use this for reference.
The atomic mass of an atom would be the number of protons PLUS the number of neutrons. Because this atom shown has 6 protons and 6 neutrons, they add up to 12. In this case, the atomic mass of this atom is 12. Atomic number is the number of protons in an atom, in this case it is 6. The atomic number is 6.