A right-angled trapezoid, the upper base is 12 meters, the lower base is 18 meters, and the two waists are 5 meters and 15 meters respectively. What is the area of this rectangular trapezoid?
一个直角梯形，上底是12米，下底是18米，两条腰分别是5米和15米．这个直角梯形的面积是多少平方米？
<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">30 * (5/2)</gadget>
<output>75</output>

<result>75</result>