( 1).( 12+ 18)×6/2=90cm？ (2)(5-2.3+5)×3.4/2 = 13.09cm？ (3)(7.2-2.2- 1.6+7.2)×4.8/2 = 25.44cm？ "/"indicates that the area formula of the divided trapezoid is (upper bottom+lower bottom) × height ÷2. Please ask me again if you have any questions. If you are satisfied, please click adopt.