(one+two+three+four+five) =24? ②
From ①-②: 65 =4,
Because there are ***20 pictures in grade five and six, and there are (20-4)÷2=8 pictures in grade five;
Level 6: 20-8= 12 (frame);
So: (one+two+three+four) =24-8= 16 (amplitude);
Because: (one+two) +4= (three+four),
The calligraphy works exhibited in Grade One and Grade Two are: (16-4)÷2=6 (pieces);
A: There are 6 calligraphy works in Grade One and Grade Two.
So the answer is: 6.