In Problems 1-3, sketch the indicated solid. Then find its volume by an iterated integration.
1. Tetrahedron bounded by the coordinate planes and the plane z = 6 - 2x - 3y
2. Tetrahedron bounded by the coordinate planes and the plane 3x + 4y + z - 12 = 0
3. Wedge bounded by the coordinate planes and the planes x = 5 and y + 2z - 4 = 0