What is Ms. Hussey's assignment, and what is Calder's first response to the assignment?

Ms. Hussey's assignment is to answer the question, "What is art?" To Calder, art is something puzzling. Calder pulls out a box given to him by his grandmother; he loves the painting that is on the cover of it. He sits in the sun, what his grandmother called a "rainbow bath," and begins to write about the box.