Answer
$1.19\text{ gallons}$
Work Step by Step
First, we calculate the total energy used per day in joules:
Energy used in W.h=$40KW.h\times\frac{1000W}{1KW}=40000W.h$
Energy used in J=$40000\frac{J}{s}\times{h}\times\frac{3600s}{h}=144000000J$
Then we convert the unit to MJ
$144000000J\times\frac{1MJ}{10^{6}J}=144MJ$
Finally, we calculate the gallons of gasoline:
$144MJ\times\frac{1gallon}{121MJ}\approx1.19\text{ gallons}$
Average car fuel economy: $\approx 25\text{ mpg}$
If a car drives $30$ miles per day → $1.2$ gallons of gasoline per day.
So, home and car use roughly similar amounts of energy per day, depending on driving habits.
