How many moles of c2h2 are needed to react completely with 84.0 mol o2?

The reaction between C2H2 and O2 is as follows:
2C2H2 + 5O2 = 4CO2 + 2H2O

After balancing the equation, the reaction ratio between C2H2 and O2 is 2:5.

The moles of O2 in this reaction is 84.0 mol. According to the above ratio, the moles of C2H2 needed to react completely with the O2 is 84.0mole *2/5 = 33.6 mole.

How many moles of C2H2 are needed to react completely with 84.0 mol O2?   

33.6 mol C2H2