Concept:In an equilateral triangle, each interior angle is 60∘.Angles on a straight line add up to 180∘.Explanation:Since △QPR is equilateral, the interior angle at R is ∠QRP=60∘.The given angle ∠PRS is the exterior angle at R, lying on a straight line with ∠QRP.So, ∠QRP+∠PRS=180∘.Substitute the known values: 60∘+(2x−10)∘=180∘.Simplify: 2x−10=120.Then 2x=130, which gives x=65.Answer:x=65, so the correct option is B.
