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How to improve the national standard in the training of the experimental class of mathematics in the fifth grade of primary school?
Connect AC like 1 building, so that the shadow part is divided into two triangles: AFC and ACE. In fact, FC is the bottom of AFC, and AB is its height. AE is the base of ACE, and CD is its height. Just add up the areas separately. (Angle b and angle d have right-angle symbols and should be right-angles. )

12* 10÷2+5* 15÷2

=60+37.5

=97.5 (square centimeter)