Connect AC, ∫≈ B ∫≈b = 90°∴AC 2 = ab 2+BC 2 = 25, then AC 2+AD 2 = 25+144 =169 =132 = CD 2, so ∠. AC+ AB？ BC= × 12×5+ ×4×3=36 square meters In this problem, the problem of solving quadrilateral is first transformed into the problem of solving triangle, and then solved by Pythagorean theorem.