Solved A small mine works two coal seams and produces three
WEBA small mine works two coal seams and produces three grades of coal. It costs £10 per hour to work to upper seam, obtaining in that time 1 tonne of anthracite, 5 tonne of best quality and 2 tonne of ordinary coal. The lower seam is more expensive to work at a cost of £15 per hour. However, it yields per hour 4 tonne of anthracite, 6 tonne of ...