There are several information's of immense importance already given in the question. Let us write them down first
Number of edges of the regular polyhedron (E) = 30
Number of vertices of the regular polyhedron (V) = 12
Let us assume the number of faces of the regular polyhedron = F
Then
V - E + F = 2
12 - 30 + F = 2
f - 18 = 2
F = 20
From the above deduction, it can be easily concluded that the number of faces of the regular polyhedron is 20.
