Using the formula si=(n.2).180 calculate the sum of the polygon below b) and then what is the value of x

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The sum of the internal angles of this polygon is 540°, and the value of the unknown x is 130.
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● But how do you know this?
● And what formula is this?
● Where:
Knowing this formula, we can solve the question:
● How do we go about figuring out the value of x ?
Good studies and I hope I have helped.