The third question: The ratio of Grade One, Grade Two and Grade Three is 3:5:6. Suppose there is 3x in the first grade, then 3x+5x+6x=56, and the solution is x=4. Senior one has done 3x=3*4= 12 (pieces).

The other two are too long to write. I hope you can think about it yourself. I really can't ask!