Answer:
20
Step-by-step explanation:
Euler's formula for polyhedra states that
F + V - E = 2
where F is faces, V is vertices and E is edges
Here F = 12, E = 30, thus
12 + V - 30 = 2, that is
V - 18 = 2 ( add 18 to both sides )
V = 20 ← number of vertices
