SARAGIH, J Erwin. Business Model Innovation for Non-formal Education Service at High School Level: A Case Study of OPSI Tutoring Center. International Journal of Business Studies, [S. l.], v. 9, n. 2, p. 149–161, 2025. DOI: 10.32924/ijbs.v9i2.382. Disponível em: https://ijbs.ipmi.ac.id/index.php/ijbs/article/view/382. Acesso em: 27 feb. 2026.