PLEASE ASAP!!

If the river flows at an average rate of 0.460 cubic feet per second, what is the additional concentration of nitrogen (expressed in milligrams of nitrogen per liter) in the river water due to the farmer's fertilizer each year? mg/L Heptane and water do not mix, and heptane has a lower density (0.684g/mL) than water (1.00g/mL). A 100 - mL graduated cylinder with an inside diameter of 3.04cm contains 40.5g of heptane and 36.1g of water. What is the combined height of the two liquid layers in the cylinder? The volume of a cylinder is r2h. where r is the radius and h is the height. cm