firstly write down the equation:
C3H8 + 5O2 = 3CO2 + 4H20
THEN Calculate the number of mole of each of them
ME OF C3H8 =44
n(C3H8) = (14.8) / 44 =0.336
n(O2) =x (calculate it )
do the same for oxygen then
followed by that
use mole ratio 1 mole of C3H8 react with 5 mole of O2,
BUT YOU USE ONLY x MOLE OF O2\
if u still have any problem please feel free...