Correct option is A
By the Euler's relation for polyhedra, We know that
F+V=E+2
Given mumber of edges = 15
Number of vertices = 10
the number of faces = x
Now putting these values in the Euler's relation, we get
F+V=E+2
x+10=15+2
x=15+2−10
x=7
3x-12 = 3×7-12=9