Based on the tiles shown, how many moles of oxygen gas (o2) are needed to produce 36.04 grams of water (h2o) when reacting with excess ethane in the equation 2c2h6 + 7o2 → 5co2 + 6h2o? three tiles

We calculate for the number of moles of water given its mass by dividing the given mass by the molar mass. 
                               n water = (36.04 g) / (18 g/mol) 
                                n water = 2 mols
From the given balanced equation, every 6 moles of water produced will require 7 moles of oxygen.
                                n oxygen = (2 mols H2O) x (7 moles O2 / 6 moles H2O)
                                n oxygen  = 2.33 mols O2