A landscaper wants to mix her own fertilizer containing a minimum of 50 units of phosphates, 240 units of nitrates, and 210 units of calcium. Brand 1 contains 1 unit of phosphates, 6 units of nitrates, and 15 units of calcium. Brand 2 contains 5 units of phosphates, 8 units of nitrates, and 6 units of calcium. Brand 1 costs $2.50 a pound; brand 2 costs $5. Express the data in equations and inequalities suitable to determine the least-cost combination of fertilizers that will meet her requirements.