Step-by-step explanation:
Atomic number (Z) = Number of the protons
It means that if the atomic number of C is 6, it implies that the number of protons in carbon is 6 too.
Mass number (M) = Number of the protons + Number of the neutrons
It means that if the atomic mass of C is 12, it implies that the number of protons and the neutrons in carbon is 12.