The cylinder is cheaper to make because it has less surface area.
Step-by-step explanation:
In order to find the surface area of a cylinder, you do 2πrh+2πr²
We need the radius, which is half of the diameter, so then we have 2π(3·12)+2π·3² which gets us 282.72
We also need the surface area of the rectangular prism which we can get by 7x4 + 7x4 + 12x7 + 12x7 + 12x4 + 12x4 which gets us 320
282.72 < 320