Propanol is C3H8O. When you burn it, each C turns into CO2, and every 2 H's turn into an H2O molecule. The rest of the balancing involves the O atoms. Without balancing the O's, you get:
C3H8O + xxx O2 --> 3 CO2 + 4 H2O. Ignoring the contribution from O2, there is one O on the left, and there are 10 on the right. That means 9 O atoms must be added to the left. Oxygen exists as O2, so 9 O atoms are equivalent to 4.5 O2's.
The equation:
C3H8O + 4.5 O2 --> 3 CO2 + 4 H2O
is balanced. It just doesn't have all of the coefficients as whole numbers, so it will be fixed by multiplying everything by two: