Hey there Kate! Here we are starting with Te atoms. We want to convert those atoms to mass, most likely to grams.
We start with 3.1 x 10^24 Te atoms, and in order to convert those atoms to grams we will need to use Avogadro's number: 6.022x10^23.
First we will convert from atoms to moles by using Avogadro's number, then from moles to grams by using the molar mass of Te (127.60 grams per mole) which you can find on the periodic table.
3.1 x 10^24 Te atoms x ( 1 mole of Te/ 6.022x10^23 atoms Te) = 5.15 moles of Te
5.15 moles of Te x ( 127.60 grams Te/ 1 mole Te) = 656.86 grams of Te.
Let us know if you have any further questions!