Tutorial Exercise cylindrical tank with radius 6 m is being filled with water at a rate of 3 m3/min_ How fast is the height of the water increasing (in m/min)? Step Let represent the radius of the cylindrical tank in m, let h represent the height of the water in the tank in m; and let V represent the volume of the water in the tank in m3 . Writing an equation for V in terms of and h gives the following result: We are given that the radius of the tank is 6 m, and therefore the radius of the column of water that is being measured remains at a constant 6 Substituting the value 6 into the volume equation gives a simplified equation for V in terms of h, as follows_ V =