Answer:
The number of sunny days in a year, and the number of houses that use solar energy in a year.
Explanation:
Since the study seeks to examine the correlation between solar output and the amount of solar energy utilized by inhabitant, a useful information to seek from the states to be included in the study are the numbers of sunny days in a year, and the number of houses that use solar energy in a year. This information can be correlated to get the result of the study.