The sum of angles of a pentagon is 540°, so x must be chosen to make that so.
85 + 110 + x + 120 + 120 = 540
540 -435 = x = 105
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The formula usually used to find the degree measure of the internal angles of an n-sided polygon is (n -2)·180°. For n=5, this is 3·180° = 540°.
