A person coughs when a foreign object is in the windpipe. The velocity of the cough depends on the size of the object. Suppose a person has a windpipe with a 25-mm radius. If a foreign object has a radius r, in millimeters, then the velocity V, in millimeters/second, needed to remove the object by a cough is given by the following equation, where k is some positive constant. For what size object is the maximum velocity needed to remove the object? V ( r ) = k (2512 - 13), Or= 25 An object that has a radius of will need maximum velocity to remove it. (Type an integer or a simplified fraction.)