Pemodelan Lapisan dan Perhitungan Sumberdaya Batubara Berdasarkan Data Log, Kualitas serta Potensinya Dimanfaatkan sebagai Briket Batubara pada Daerah Sekitar Subanburung, Formasi Muara Enim, Sumatera Selatan = Modeling Layers and Calculation of Coal Resources Based on Log Data, Quality, and Their Potential for Utilization as Coal Briquettes in the Surrounding Area of Subanburung, Muara Enim Formation, South Sumatra