A rectangular prism is completely packed with 54 cubes of edge length fraction 1 over 2 inch, without any gap or overlap. Which of these best describes the volume of this rectangular prism?
6 unit cubes and 6 smaller cubes of volume fraction 1 over 8 cubic inch each
13 unit cubes and 4 smaller cubes of volume fraction 1 over 8 cubic inch each
6 unit cubes and 3 smaller cubes of volume fraction 1 over 8 cubic inch each
13 unit cubes and 2 smaller cubes of volume fraction 1 over 8 cubic inch each