A mixture of composition of 70.0% methane (CH4) and 30 % ethane (C2H6) by mass is burned up in oxygen to produce carbon dioxide and water. The reactions that occur are CH4 + 2 O2 = CO2 + 2 H2O and 2 C2H6 + 7 O2 = 4 CO2 + 6 H2O. How many grams of oxygen are needed to react completely with 50.0 grams of the hydrocarbon mixture?