A solid is contructed so that one side is the region between the lines x=a\displaystyle {x}={a}, x=b\displaystyle {x}={b}, the graph of y=f(x)\displaystyle {y}={f{{\left({x}\right)}}} and the x-axis, and the cross-sections of the solid perpendicular to the x-axis are rectangles with base 8 (as shown in the figure).

Which of the following integrals represents the volume of this solid?