The Equation of reaction
C + O2 === CO2
First Blank spot would be
---- 3.5moles of O2
2nd spot
Up.... 1mole of CO2
Down ---- 2moles of Oxygen atoms
3rd spot
Up... --- 22.4L of CO2(1mole of any gas at STP contains 22.4L)
Down---- 1mole of CO2
Final answer --- 3.5 x 1/2 x 22.4
=39.2L of CO2