Ok so this problem pissed me off to no end... basically because ih ad 5 minutes to do it and couldn't figure it out.

Now, i divided the 120g by the molar mass of PF3 and divided by .846 to find the actual amount necessary which gave me 1.612449659 moles. Multply that by the molar mass of F2 and i get 61.26663726. Wasn't correct, wasn't even a matter of significant figures... what went wrong here :D

oh damn it. They were constantly giving me pre-balanced equations and having to do this so i never noticed that they gave me an unbalanced equation....