Question

How many GRAMS of boron are present in 3.54 moles of boron trifluoride

Answer 1

How many mols of BF3 do you have? That's 3.54. How many mols B are in that. Since there is 1 mol B atoms in 1 mol BF3 molecules, there must be 3.54 x 1 = 3.54 mols B atoms.
Now convert mols B to grams with g B = mols B x atomic mass B.

Answer 2

38.26