Question: how to figure out how many atoms are there?
Answer: Mass → Moles and Moles → Atoms.
196.967 u . ... 
So, if you are given the mass of an element, you use the periodic table to find its molar mass, and multiply the given mass by the reciprocal of the molar mass. ... 
Once you have moles, multiply by Avogadro's number to calculate the number of atoms.