Question

I need help finding the radius of this cross section.
In this problem we will look at properties of solids with base on the x-y plane given by the circle x^2 + y^2 = a^2 and its interior, where \, a>0 \

(i) Let a=6, and assume that cross-sections of the solid perpendicular to the x-axis are circular disks with diameters lying in the x-y plane. Find the area A(x) of the cross-section at location ,x