Hey there!:
Temperature in kelvin : 45 + 273 => 318 K
Number of moles H2:
p * V = n * R * T
4.46 * 0.579 = n * 0.082 * 318
2.58234 = n * 26.076
n = 2.58234 / 26.076
n = 0.09903 moles of H2O
Given the reaction:
XeF6(s) + 3 H2(g) → Xe(g) + 6 HF(g)
Molar mass XeF6 = 245.3 g/mol
0.09903 mol H2O * ( 1 mol XeF6 / 3 mol H2 ) * 245.3
= 8.09 g of XeF6
Hope that helps