What percent by mass of each chloroform molecule is composed of chlorine?

So chloroform is CHCl3 so the first thing we need to do is find out what the mass in amu of one atom of chloroform:
12.01amu(C)+1.008amu(H)+3*35.45amu(Cl3)=119.368amu
Then we find the amu of the Cl in the molecule which is 3*35.45amu=106.35amu
Then to find the percent by mass we take the mass of the 3 Cl divide it by the total mass of the molecule and multiply by 100.
so 106.35/119.368=0.89094 and 0.89094*100=89.094%
so the percent by mass of each chloroform molecule that is composed of chlorine is 89.094%!
I hope this helps!