Answer:
30
Step-by-step explanation:
Using Euler's relationship for polyhedra
F + V - E = 2
F is number of faces, V number of vertices, E number of edges
Rearrange to express E as the subject
Add E to both sides
F + V = E + 2 ( subtract 2 from both sides )
F + V - 2 = E ← substitute values
20 + 12 - 2 = E, hence
E = 30
