A fast$-$food restaurant uses $3,500$ kilograms of hamburger meat each week. Thirty percent of this hamburger meat is certified organic. The manager of the restaurant wants to ensure that the meat is always fresh, especially the organic meat which has a low shelf life. To maintain its high standards, the restaurant insists on using organic hamburger meat which is no more than two days old on average. How much certified organic hamburger meat should be kept in the refrigerator as inventory, on average?