请详细讲解这道题---**Extraction Content:** **Question Number:** 8 **Question Stem:** 如图，在四边形 ABCD 中，∠A+∠B=150°，点 E 为 AB 的中点，AD=2，BC=4，则 **Expression to Evaluate:** S△ADE + S△BCE - S△CDE = ______ **Given Information:** * Figure shows a quadrilateral ABCD. * ∠A + ∠B = 150° * E is the midpoint of AB. * AD = 2 * BC = 4 **Chart/Diagram Description:** * Type: Geometric figure. * Main Elements: * Points A, B, C, D, E. * Line segment AB with point E located on it, between A and B. * Segments AD, BC, CD, AC, BD, DE, CE are drawn. * The figure shows a quadrilateral ABCD, divided into triangles by lines from E to D and C. Triangles ADE, BCE, and CDE are formed. * Points A, E, B appear collinear, forming the base of the figure. D is positioned above and to the left of AB. C is positioned above and to the right of AB.