Iron is produced by reduction from its ore according to the reaction

Fe2O3(s) + 3 H2(g) --> 2 Fe(s) + 3 H2O(g)

How many liters of H2 gas are required to completely react with 34.2 g of Fe2O3 at 754.3 mm Hg and a temperature of 723 K?

Trying to learn so please explain, thanks in advance :)