As per the problem 2 moles of propane are produced when 7 moles of carbon are supplied
so if we supply 1 mole of carbon the moles of propane obtained = 2 /7
if we supply 1.4 moles of carbon the moles of propane obtained = 2 X 1.4 /7 = 0.4 moles of propane
Hence answer is propane we can produce using this reaction = 0.4 moles from 1.4 moles of carbon