Theoretical Yield Please Help!!!

Sep 2015
7
0
The reaction of 3.0 mol of hydrogen gas with excess fluorine gas produced hydrogen fluoride gas (20.01 g/mol) as shown in the balanced chemical equation below.

Determine the theoretical yield in grams for this reaction.
H2(g) + F2(g) → 2HF(g)

I know the answer is 120 g but how do you get to that answer.