Answer:
x = 50
Explanation:
The sum of the interior angles of a quadrilateral = 360°
Therefore, add together the expressions for all 4 angles, equal to 360, and solve for x:
(2x + 15) + (3x - 20) + x + (x + 15) = 360
Gather like terms: 2x + 3x + x + x + 15 - 20 + 15 = 360
Combine like terms: 7x + 10 = 360
Subtract 10 from both sides: 7x = 350
Divide both sides by 7: x = 50