A well of radius 7 meters is dug out in the shape of a cylinder such that the curved surface area of the well (excluding embankment) is 2640 sq meters. Out of the total mud taken out in this process, 1320 cubic meters of mud is thrown away and the rest is used to make an embankment (of constant width) around the well such that the height of the embankment is 21 meters. What is the width (or) thickness of the embankment?