2C8H18 + 25O2 ----> 16CO2 + 18H2O
2 moles of octane gives 16 moles of CO2
so 1 mole of octane will give = 16/2 = 8 moles of CO2
so 603 moles of octane will give 8 X 603 = 4824 moles of CO2
now use PV = nRT
P = 0.995 atm
V = ? L
n = 4824
R = 0.0821 L atm/K/mole
T = 28 + 273 = 301 K
0.995 X V = 4824 X 0.0821 X 301
V = 4824 X 0.0821 X 301/ 0.995 = 119810.22 L