Roslan, Nur Izzati Nabilla, et al. “Implementation of Economic Scale for Contractors Grade 5 to Grade 7 During Covid-19 Pandemic”. Multidisciplinary Applied Research and Innovation, vol. 3, no. 1, Feb. 2022, pp. 338-45, https://publisher.uthm.edu.my/periodicals/index.php/mari/article/view/4052.