An important information, specifically a constant, we need to know is the Avogadro's number. Avogadro's number is equal to 6.022*10^23 mol^-1.
This is the constant we use to convert atoms to moles. So we need to divide 7.83 x 10^24 atoms with the Avogadro's number to get the number of moles. That will be equal to 13 moles of He. Then to convert moles to grams we need the molar mass of Helium (4 grams/mole). We then multiply the number of moles with the molar mass of Helium. We would have 52 grams of Helium.
