Use euler’s formula to find the missing number.
edges: 49
faces: 21
vertices: ?

30
32
26
28

Option 1st is correct

number of vertices = 30

Step-by-step explanation:

Let e be the number of edges, f be the number of faces and v be the number of  vertices.

As per the statement:

Number of edges(e) = 49

Number of faces(f) = 21

We have to find number of vertices.

using Euler's formula:

then;

⇒

Add 28 to both sides we have;

Therefore, the number of vertices = 30

take the logarithm of both sides (the base of the log doesn't matter):

apply the exponent property - this says that :

distribute the log terms on both sides:

group like terms together:

divide through both sides by the coefficient on :

you can do some additional rewriting here using the properties of the logarithm to simplify things if you like: