A farmer can buy two types of plantfood, mix A and mix B. Each cubic yard of mix A contains 20 pounds of phosphoricacid, 30 pounds ofnitrogen, and 5 pounds of potash. Each cubic yard of mix B contains 10 pounds of phosphoricacid, 30 pounds ofnitrogen, and 10 pounds of potash. The minimum monthly requirements are 420 pounds of phosphoricacid, 960 pounds ofnitrogen, and 220 pounds of potash. If mix A costs $25 per cubic yard and mix B costs $40 per cubicyard, how many cubic yards of each mix should the farmer blend to meet the minimum monthly requirements at a minimumcost? What is thiscost?