The economic activity among the given options is the payment of school fees. An economic activity is any activity that involves the production, distribution, and consumption of goods and services to satisfy the needs and wants of people. In this case, paying school fees involves the exchange of money for the service of education. Education is a service that is produced by schools and consumed by students. By paying school fees, parents or guardians are contributing to the production and distribution of education, which is an essential service for human development and progress. In contrast, attending a town's meeting, visiting a stadium, and arresting a petty thief do not directly involve the production or consumption of goods and services and are therefore not considered economic activities.