If you were given a question like below:
What is the mass in grams of a sample of $\ce{Fe2(SO4)3}$ that contains $3.59 \times 10^{23}$ sulfate ions, $\ce{SO4^{2−}}$ ? The molar mass of $\ce{Fe2(SO4)3}$ is $399.91 \, \text{g}/\text{mol}$.
How would you go about solving a question like that?
I'm confused about how to use only the quantity of sulfate ions to find the mass in grams of the whole sample, given it's grams per mole.