Answer is: 13.7 grams of water.
N(H₂O) = 4.589·10²³; number of water molecules.
n(H₂O) = N(H₂O) ÷ Na(Avogadro constant).
n(H₂O) = 4.589·10²³ ÷ 6.022·10²³ 1/mol.
n(H₂O) = 0.76 mol; amount of substance.
M(H₂O) = 2 · Ar(H) + Ar(O) · g/mol.
M(H₂O) = 2 · 1 + 16 · g/mol.
M(H₂O) = 18 g/mol; molar mass of water.
m(H₂O) = n(H₂O) · M(H₂O).
m(H₂O) = 0.76 mol · 18 g/mol.
m(H₂O) = 13.7 g.