Situmeang, R. R., A. Antoni, J. Patricia, and D. Reinaldo. “The Influence of Service Quality, Distribution Channels, and Promotion on Sales Volume at PT Delta Agro Makmur Medan”. Jurnal Mantik, vol. 4, no. 2, Aug. 2020, pp. 1356-60, doi:10.35335/mantik.Vol4.2020.950.pp1356-1360.