Laila, E., and A. Ulianas. “ANALISIS PENYEBAB KESULITAN SUB MATERI POKOK KIMIA SEMESTER 1 KELAS X IPA 3 MENGGUNAKAN METODE LEAN SIX SIGMA DI SMA NEGERI 8 PADANG”. Ranah Research : Journal of Multidisciplinary Research and Development, Vol. 1, no. 4, Aug. 2019, pp. 1139 -47, https://jurnal.ranahresearch.com/index.php/R2J/article/view/183.