For the number of protons, we look at the atomic number of the element given. Take note that atoms must have equal numbers of protons and electrons. For the number of neutron, we must know the mass number. To find the mass number, all we need to do is round the atomic weight to the nearest whole number (if the atomic weight is given).
After knowing what the mass number is, we use the formula below to calculate the number of neutrons.
Mass Number = (Number of Protons) + (Number of Neutrons).