A large container has the shape of a frustum of a cone with top radius 5 m, bottom radius 3 m, and height 12 m. The container is being filled with water at the constant rate of 3.2 m³/min. At what rate is the level of water rising at the instant the water is 7 m deep? Note: A frustum of a cone is the portion of a cone between two parallel planes. For example, the popular coffee cup has the shape of a frustum of a cone. The water is rising at the rate of cm/min. (Round to one decimal place as needed.)