Stroika Concrete makes bags of easy-use concrete for the DIY market. The company mixes their concrete using two ingredients, "Great Grit" and "A1 Aggregate". Great Grit costs L1 per kilogram and consists of 20% fine sand, 40% coarse sand and 40% gravel. A1 Aggregate costs L0.75 per kilogram and consists of 10% fine sand, 50% coarse sand and 40% gravel. Each bag of Stroika concrete must contain at least 2kg of fine sand, 2 kg of coarse sand and 6 kg of gravel. What is the least cost combination of ingredients that will satisfy the minimum requirements, and what will be the cost of these ingredients per bag of concrete produced?