Answer:
The explanatory variable is:
period of usage.
Explanation:
As the explanatory variable, the period of usage of the car does not depend on the maintenance cost or its performance. Instead, the maintenance cost and the performance of the automobile, which are response or dependent variables, depend on the period of usage. Period of usage (time) is always an independent or explanatory variable. In this organization, the performance of the automobile does not depend on the maintenance cost, but the two dependent variables (performance and maintenance cost) depend on the period of usage.