Answer
See answer below.
Work Step by Step
Enthalpies of formation (kJ/mol):
$H_2O(l):-285.83, CO_2(g): -393.509, CH_3OH(l): -238.4, C_8H_{18}(l): -259.3$
Methanol:
$(-393.509+2\times-285.83- -238.4)\ kJ/mol\div32.04\ g/mol=-22.68\ kJ/g$
Isooctane:
$(8\times-393.509+9\times-285.83- -259.3)\ kJ/mol\div 114.23\ g/mol=-47.81\ kJ/g$
Gasoline provides over twice the amount of energy per unit of mass.
