For starters, it's worth pointing out that you're not dealing with molecules of iron(III) fluoride here because this compound is ionic.
So a more accurate statement here would be that the problem wants you to find the number of formula units of iron(III) fluoride present in that sample.
Now, the key here is the molar mass of iron(III) fluoride, which you will find listed as
Since you know that the molar mass of the compound tells you the mass of exactly
You should also know that Avogadro's constant tells you that you need
So if you know that
#24 color(red)(cancel(color(black)("g"))) * (6.022 * 10^(23) quad "formula unit FeF"_3)/(112.84color(red)(cancel(color(black)("g")))) = color(darkgreen)(ul(color(black)(1.3 * 10^(23) quad "formula units FeF"_3)))#
The answer is rounded to two sig figs, the number of sig figs you have for the mass of iron(III) fluoride.