Asolid has faces that consist of 5 congruent squares and 4 congruent equilateral triangles. the solid has 9 vertices. how many edges does the solid have? (no image)
a.
16 edges
b.
18 edges
c.
20 edges
d.
22 edges

The answer is A. 16 edges

Euler's polyhedron formula:
f + v - e = 2
f - the number of faces
v - the number of vertices
e - the number of edges

f = 5 congruent squares + 4 congruent equilateral triangles = 9
v = 9
e = ?

f + v - e = 2
e = f + v - 2
e = 9 + 9 - 2
e = 16