Pemodelan lapisan batu bara guna estimasi sumber daya batu bara dan analisis kualitas batu bara pada Lapangan Banko Barat PIT X PT. Bukit Asam, Tbk., Tanjung Enim, Sumatera Selatan = Modeling of coal seams to estimate coal resources and analysis of coal quality in the West Banko Field PIT X PT. Bukit Asam, Tbk., Tanjung Enim, South Sumatra