Volumes of Solids by Cross-Section

Which expression represents the vertical distance between both curves anywhere within the shaded region?

Which expression represents the area of any square within the shaded region whose base is perpendicular to the x-axis?

Which expression represents the volume of a solid created by an infinite amount of squares whose bases are perpendicular to the x-axis?

Which expression represents the radius of any circle within the shaded region whose diameter is perpendicular to the x-axis?

Which expression represents the area of any semicircle within the shaded region whose diameter is perpendicular to the x-axis?