<span>These types of lines are called contour lines. Though the image is flat and on a two dimensional sheet of paper, they suggest the volume of the shape. Such drawings are often done very quickly or with a single hand motion.</span>
The curves
and
intersect at approximately
. The area is then
1: 8 faces and 9 with the base 9 vertices and 16 edges
2: 3 faces and 5 with the bases 6 vertices and 9 edges
3: 3 faces and 4 with the base 4 vertices and 6 edges
Hope this can help you.
