In Exercises 11-13 use Euler's Formula F + V = E + 2 to find the number of faces, edges or vertices.

11. a prism has 6 faces and 8 vertices. How many edges does it have?
12. A pyramid has 4 faces and 4 vertices. How many edges does it have?
13. A pyramid has 8 edges and 5 vertices. How many edges does it have?