Hidayat, P. W., S. M. E. Susilowati, and E. Ellianawati. “Analysis of Problem-Solving Abilities of Elementary School Students Through Problem-Based Learning Model Based on Self Confidence”. Journal of Primary Education, Vol. 8, no. 4, Jan. 2019, pp. 8-15, https://journal.unnes.ac.id/sju/jpe/article/view/28237.