The answer would be 21 because its the same length as the other side.
The sum of the inner angles of a polygon with n sides is 
Since your polygon has 6 sides, the sum of its inner angles has to be

On the other hand, the sum of its inner angles is

And it has to be 720, so we have

Answer:
<h2>cant understand this language so sorry</h2>
Step-by-step explanation:
<h3>so sorry</h3>
A) is the anwser to the question