The chang's neighbor owns a ready-mix company. the company receives an order for 12.5 cubic yards of concrete. this mixture of concrete contains sand, cement, gravel, and water. for each pound of water, there are 5.5 pounds of sand, 2 pounds of cement, and 7.5 pounds of gravel. determine how many pounds of cement must be used. assume a cubic yard of concrete weighs 4,000 pounds.