In Chemistry, the Periodic Table is the source of all knowledge. Look on it for the information you need.
B = 11 grams / mol
F = 19 grams / mol
This stuff has a formula of BF3.
The 3 only affects the F. There is 1 Boron and 3 florines. If you want a number to affect the Boron, use brackets. In this case, we don't.
BF3 = 11 + 3*19 = 11 + 57 = 68 grams / mol
Molar Mass BF3 = 68 grams /mol <<<< ==== answer