You can find this on google easily
Density is weight by volume.
First. If you divide the weight by density you can find the volume
Second you must convert the ML in to Liters.

1L=1000ml


0.38214 Liters.
2H₂₍g₎ + O₂ ₍g₎→ 2H₂O
138 mol H₂ × (2 mol H₂O ÷ 2 mol H₂)= 138 mol H₂O
64 mol O₂ × (2 mol H₂O ÷ 1 mol O₂)= 128 mol H₂O
128 mol H₂O
I think it is C. coefficients but I don't know what subscripts are