et.al, H.J.S. 2021. Marketing Management Concept and Coaching of Leadership Methods in Operations Management of Companies: Case Study of Cellular Telecommunications Companies in Medan City. Turkish Journal of Computer and Mathematics Education (TURCOMAT). 12, 13 (Jun. 2021), 4350–4357. DOI:https://doi.org/10.17762/turcomat.v12i13.9477.