The balanced chemical reaction:
WO3+3H2-->W+3H2O
We are given the amount of tungsten trioxide to be used in the given reaction. This will be the starting point for our calculations.
5.10 g WO3 (1 mol W / 183.84 g W) ( 1 mol WO3 / 1 mol W ) ( 231.8 g WO3 /1 mol WO3 ) = 6. 43 g WO3