assuming the rest of your math is correct, the cone would have an area of roughly 212 sq in and the bowl roughly 157 sq inches. Therefore the one with less area is cheaper to make
12-8 over 6-2= 4 over 4= 1
The slope is 5/3 and the y- intercept is -2/3

Actually Welcome to the concept of Surface Areas and Volume.
==> Volume of Cylinder = πr^2h
==> 27π = πr^2(3)
==> 27 = r^2 (3)
==> r^2 = 9
==> r = 3 inch
hence the radius is 3 inches.