this is the solution to the combustion question:
Heat = -0.21 x 4.18 x 10^3 x 65
=57057J
=57.057kJ
n=57.057/1367
=0.0417mol
then you times this number by 2 as twice as many moles of ethanol is needed to achieve the heat energy of 57.057
=0.0834mol
then using n=m/Mm
m=...