In △OTS: ∠OST = 90° (radius ⊥ tangent), so 3x° + x° + 90° = 180° → 4x = 90° → x = 22.5°. Therefore, 2x° = 45°.
Option B
Since OS is a radius and TS is a tangent, ∠OST = 90° (Theorem 10.1). The angles of △OTS sum to 180°: 3x + x + 90 = 180 → x = 22.5, so 2x = 45. Always apply the radius-tangent perpendicularity property first in such problems.