Question: Calculus excercise with maple

Excuse me for my English, I'm Dutch)    

I have a excersice I have to make in Maple, but i don't have a clue on how to do it. I will just type it here and see what the response is.

If somebody has the Calculus book written by James Stewart, it's the "Discovery Project" on page 1040..

The figure shows the solid enclosed by three circular cylinders with the same diameter that intersect at right angles/ In this project we compute its volume and determine how its shape changes if the cylinders have different diameters.

1. Sketch the solid enclosed by the three cylinders x+ y = 1, x+ z = 1, y+ y = 1.

2. Find the volume of the solid in Problem 1.

3. Use a CAS to draw the edges of the solid.

4.What happens to the solid in Problem 1 if the radius of the first cylinder is different from 1? Illustrate with a computer graph

5. If the first cylinder is x+ y = a where a<1, set up a double integral for the volume of the solid. What if a>1?

That's the excersice. i hope someone could help me. Because I'm really stuck. Thanks in advance.