Fundamentals E3 Practice problem

[jackiee37]

In a nanotechnology lab you might have the capability to manipulate individual atoms. The atoms on the left are gallium atoms (molar mass 70 g.mol^-1), and those on the right are atoms of astatine (molar mass 210 g.mol^-1). How many astatine atoms would the pan on the right have to contain for the masses on the two pans to be equal?

How can I solve this? (There is also a image in this question)

[morgan 1I]

Astatine atoms are 3x as massive as gallium atoms, so we need 3x the amount of gallium atoms to make the masses equal. There are 9 gallium atoms on the left, and by dividing that by 3, we get the amount of astatine atoms that would make the masses equal.