Geometry

Question Analysis:
This question involves angle relationships in an isosceles trapezoid using expressions with variables.
The main focus is using the fact that each pair of adjacent angles between the parallel sides is supplementary.

Key Concept Explanation:
In any trapezoid, a base angle and the top angle directly above or below it are supplementary (they add up to 180°).
In an isosceles trapezoid, the base angles are equal, and the top angles are equal.

Step-by-Step Solution:
Each adjacent pair (e.g., angle A and angle D) adds to 180°.
So: (3x + 15) + (x + 25) = 180
Combine like terms: 4x + 40 = 180
Solve for x: 4x = 140 → x = 35