RS Aggarwal Solutions for Class 9 Chapter 15 “Volumes-and-surface-area-of-solids”, the surface area is the area that describes the material that will be used to cover a geometric solid. When we determine the surface areas of a geometric solid, we take the sum of the area for each geometric form within the solid. The volume is a measure of how much a figure can hold and is measured in cubic units. Surface area is used in finding out the outside areas of machines and is essential in chemical experiments. Volume is used to find the amount of liquid in a bowl or the capacity of the vessel to carry liquid. This chapter deals with formulas and various methods which are used in finding volume and surface area of cuboid, cubes, cylinders, right circular cone, sphere, spherical shell and hemisphere.