Pengaruh Model Pembelajaran Berbasis Masalah terhadap Kemampuan Berpikir Kritis Siswa SMP Materi Sistem Persamaan Linear Dua Variabel: The Effect of Problem-Based Learning Model on the Critical Thinking Ability of Junior High School Students Two-Variable Linear Equation System Material (LPPM Universitas Hasyim Asy'ari Lembaga Penelitian dan Pengabdian Masyarakat, 2024)