Concept:A polygon with four angles is a quadrilateral, and the sum of its interior angles is 360∘.Explanation:The given angles are 2x, 5x, x, and 4x.Since these are the four angles of a quadrilateral, their sum is 360∘.So, write the equation: 2x+5x+x+4x=360∘.Add the like terms: 12x=360∘.Divide both sides by 12: x=12360∘.Therefore, x=30∘.Answer:x=30∘, which is option B.