Because two pieces of calligraphy must be adjacent and tied together.
have
A (2,2) * A (2,2) = 2 * 2 = 4 kinds.
Paintings can't be adjacent, and then illustrate between calligraphy and design.
There are three spaces, insert two pictures, and there are a (3,2) = 6 kinds.
A total of 4*6=24 species.