Answer
100000 homes
Work Step by Step
We can write,
$U=\frac{5}{2}nRT=\frac{5}{2}PV$ for the air.
Let's plug known values into this equation.
$U=\frac{5(7.7\times10^{6}Pa)(5.6\times10^{5})}{2}=107.8\times10^{11}J$
Let's find the energy consumed per day by one house in joules.
$30\space kWh=(30000\frac{J\space h}{s})(\frac{3600\space s}{1\space h})=1.08\times10^{8}J$
Number of homes = $107.8\times10^{11}J(\frac{1\space home}{1.08\times10^{8}J})=100000\space homes$
