The Equation is CaH2(s)+2H2O(l)-->Ca(OH)2(aq)+2H2(g)
so,
moles of H2 generated = PV / RT
R = 62.363 L Torr K−1 mol−1
number of moles = 814 * 53.5 / 62.363 * 293
= 2.38 moles
looking at the equation these came from 2.38 /2 moles of CaH2 or 1.19 moles
Molar mass of CaH2 is 42.0943 g/mol
so mass of CaH2 = 1.19 X 42.1 = 50.01g