Iron has an atomic number of 26. That means iron has 26 protons and 26 electrons. With those numbers, the atom is neutral. In order to know how many neutrons are in an atom, you must know the mass number. The mass number is the total number of protons and neutrons in an atom. Once you know the mass number, subtract how many protons are in the atom from that mass number. That number is the answer to how many neutrons are in the atom.
The easiest way to find the mass number is to round the atomic mass of the atom to the nearest whole number. Iron's average atomic mass is 55.845. That rounds to 56. 56 is iron's mass number. 56 - 26 protons = 30. A typical iron atom has 30 neutrons.