I assume you mean to ask how to find the sum of the seven terms?
You have



...

So the sum is

You know that

and

, so the sum is equal to
Answer:
Step-by-step explanation:
Sum of all angles of triangle = 180
39 + 102 + x = 180
141 + x = 180
Subtract 141 from both sides
x = 180 - 141
x = 39