There is a point where the smallest cut in front and slither polymer the most difficult. Therefore, in order to calculate the speed at which an area in front of the cutting point of a polymer can be flowing in every area.
A point is a point with minimal cross-sectional area and Polymer flow hardest. Therefore, in order to calculate the speed at which the cross-sectional area A Polymer can flow in all areas.
A point is the point of having minimal cross sectional area and polymer flow in the most difficult. So in the calculation of the fast cross sectional area at that point a polymer can flow in every area.